fix: raise test-go-pg timeout budget, lower macOS parallelism (#27997)

`test-go-pg (macos-latest)` has recurred three times on
[coder/internal#1365](https://github.com/coder/internal/issues/1365),
most
recently as the `cli` package hitting its own `go test -timeout 20m`
after
several minutes of runner-side scheduling delay, which marks hundreds of
in-flight subtests as failed instead of surfacing the actual cause.

Raise `GOTEST_FLAGS -timeout` from `20m` to `25m` and the matching
`timeout-minutes` on every job that shares it (`test-go-pg`,
`test-go-pg-17`, `test-go-race-pg` in `ci.yaml`; `flake_go` in
`flake-go.yaml`; `test-go-pg` in `nightly-gauntlet.yaml`) from `25` to
`30`, preserving the 5-minute margin that lets `go test`'s own timeout
fire before GitHub cancels the job and produce a goroutine dump for a
genuine hang.

Also lower macOS `test-parallelism-tests` from `16` to `8`, matching
Linux, to test whether the 2x core oversubscription is contributing
scheduler contention. Windows keeps `16`; nothing in the current
evidence
implicates it.

This is a mitigation, not a confirmed root cause; the runner scheduling
delay itself is still unexplained.

Refs coder/internal#1365

## AI disclosure

Per [AI Contribution
guidelines](https://coder.com/docs/about/contributing/AI_CONTRIBUTING):
this PR was primarily authored by Claude Code, directed by @BobbyHo,
based
on triage of the linked ticket's CI-flake-bot comments and a review of
the
current `Makefile`/`ci.yaml`/`flake-go.yaml`/`nightly-gauntlet.yaml`
timeout configuration.

**Verification:**

- `make lint/actions/actionlint` and `make lint/actions/zizmor` both
pass
  clean on the three edited workflow files.
- `make pre-commit` passes (includes `make gen`, `make fmt`, `make
lint`,
  and a full local build).
- All three edited workflow YAMLs parse (`ruby -ryaml`) and
  `make -n test TEST_PACKAGES="./cli/..."` confirms `GOTEST_FLAGS`
  resolves to `-timeout 25m` as intended.
- This is a config-only change (no application code touched); the
  intended effect can only be confirmed by watching real `test-go-pg`
(macOS) runs on this PR and on `main` after merge, since the underlying
  runner-stall failure is intermittent.

.github/workflows/ci.yaml

@@ -527,7 +527,7 @@ jobs:
     # `make test` to ensure we receive a trace of running goroutines.
     # Setting this to the timeout +5m should work quite well even if
     # some of the preceding steps are slow.
-    timeout-minutes: 25
+    timeout-minutes: 30
     strategy:
       fail-fast: false
       matrix:
@@ -662,11 +662,12 @@ jobs:
         uses: ./.github/actions/test-go-pg
         with:
           postgres-version: "13"
-          # Our macOS runners have 8 cores.
-          # Even though this parallelism seems high, we've observed relatively low flakiness in the past.
-          # See https://github.com/coder/coder/pull/21091#discussion_r2609891540.
+          # Our macOS runners have 8 cores. test-parallelism-tests matches
+          # Linux's rather than the previous 16, to rule out scheduler
+          # contention as a contributor to the macOS test-go-pg timeouts
+          # tracked in coder/internal#1365.
           test-parallelism-packages: "8"
-          test-parallelism-tests: "16"
+          test-parallelism-tests: "8"
           # By default, run tests with cache for improved speed (possibly at the expense of correctness).
           # On main, run tests without cache for the inverse.
           test-count: ${{ github.ref == 'refs/heads/main' && '1' || '' }}
@@ -737,7 +738,7 @@ jobs:
     # `make test` to ensure we receive a trace of running goroutines.
     # Setting this to the timeout +5m should work quite well even if
     # some of the preceding steps are slow.
-    timeout-minutes: 25
+    timeout-minutes: 30
     steps:
       - name: Harden Runner
         uses: step-security/harden-runner@bf7454d06d71f1098171f2acdf0cd4708d7b5920 # v2.20.0
@@ -808,7 +809,11 @@ jobs:
     runs-on: ${{ github.repository_owner == 'coder' && 'depot-ubuntu-22.04-16' || 'ubuntu-latest' }}
     needs: changes
     if: needs.changes.outputs.go == 'true' || needs.changes.outputs.ci == 'true' || github.ref == 'refs/heads/main'
-    timeout-minutes: 25
+    # This timeout must be greater than the timeout set by `go test` in
+    # `make test-race` to ensure we receive a trace of running goroutines.
+    # Setting this to the timeout +5m should work quite well even if
+    # some of the preceding steps are slow.
+    timeout-minutes: 30
     steps:
       - name: Harden Runner
         uses: step-security/harden-runner@bf7454d06d71f1098171f2acdf0cd4708d7b5920 # v2.20.0

.github/workflows/flake-go.yaml

@@ -25,9 +25,9 @@ jobs:
     name: Flake Check
     runs-on: ${{ github.repository_owner == 'coder' && 'depot-ubuntu-22.04-4' || 'ubuntu-latest' }}
     # This timeout must be greater than the Go test timeout set in `make test`
-    # (-timeout 20m) so we receive a goroutine trace before the runner kills
+    # (-timeout 25m) so we receive a goroutine trace before the runner kills
     # the job. Mirrors the test-go-pg job in ci.yaml.
-    timeout-minutes: 25
+    timeout-minutes: 30
     steps:
       - name: Harden Runner
         uses: step-security/harden-runner@bf7454d06d71f1098171f2acdf0cd4708d7b5920 # v2.20.0

.github/workflows/nightly-gauntlet.yaml

@@ -19,7 +19,7 @@ jobs:
     # `make test` to ensure we receive a trace of running goroutines.
     # Setting this to the timeout +5m should work quite well even if
     # some of the preceding steps are slow.
-    timeout-minutes: 25
+    timeout-minutes: 30
     strategy:
       fail-fast: false
       matrix:
@@ -98,9 +98,12 @@ jobs:
         uses: ./.github/actions/test-go-pg
         with:
           postgres-version: "13"
-          # Our macOS runners have 8 cores.
+          # Our macOS runners have 8 cores. test-parallelism-tests matches
+          # Linux's rather than the previous 16, to rule out scheduler
+          # contention as a contributor to the macOS test-go-pg timeouts
+          # tracked in coder/internal#1365.
           test-parallelism-packages: "8"
-          test-parallelism-tests: "16"
+          test-parallelism-tests: "8"
           test-count: "1"
           embedded-pg-path: "/tmp/tmpfs/embedded-pg"
           embedded-pg-cache: ${{ steps.embedded-pg-cache.outputs.embedded-pg-cache }}