chore: run test-go-pg on macOS and Windows in regular CI (#17853)

This PR starts running test-go-pg on macOS and Windows in regular CI.
Previously this suite was only run in the nightly gauntlet for 2
reasons:

- it was flaky
- it was slow (took 17 minutes)

We've since stabilized the flakiness by switching to depot runners,
using ram disks, optimizing the number of tests run in parallel, and
automatically re-running failing tests. We've also [brought
down](https://github.com/coder/coder/pull/17756) the time to run the
suite to 9 minutes. Additionally, this PR allows test-go-pg to use cache
from previous runs, which speeds it up further. The cache is only used
on PRs, `main` will still run tests without it.

This PR also:

- removes the nightly gauntlet since all tests now run in regular CI
- removes the `test-cli` job for the same reason
- removes the `setup-imdisk` action which is now fully replaced by
[coder/setup-ramdisk-action](https://github.com/coder/setup-ramdisk-action)
- makes 2 minor changes which could be separate PRs, but I rolled them
into this because they were helpful when iterating on it:
- replace the `if: always()` condition on the `gen` job with a `if: ${{
!cancelled() }}` to allow the job to be cancelled. Previously the job
would run to completion even if the entire workflow was cancelled. See
[the GitHub
docs](https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/evaluate-expressions-in-workflows-and-actions#always)
for more details.
- disable the recently added `TestReinitializeAgent` since it does not
pass on Windows with Postgres. There's an open issue to fix it:
https://github.com/coder/internal/issues/642

This PR will:

- unblock https://github.com/coder/coder/issues/15109
- alleviate https://github.com/coder/internal/issues/647

I tested caching by temporarily enabling cache upload on this PR: here's
[a
run](https://github.com/coder/coder/actions/runs/15119046903/job/42496939341?pr=17853#step:13:1296)
showing cache being used.

.github/actions/setup-go/action.yaml

@@ -8,42 +8,26 @@ inputs:
   use-preinstalled-go:
     description: "Whether to use preinstalled Go."
     default: "false"
-  use-temp-cache-dirs:
-    description: "Whether to use temporary GOCACHE and GOMODCACHE directories."
-    default: "false"
+  use-cache:
+    description: "Whether to use the cache."
+    default: "true"
 runs:
   using: "composite"
   steps:
-    - name: Override GOCACHE and GOMODCACHE
-      shell: bash
-      if: inputs.use-temp-cache-dirs == 'true'
-      run: |
-        # cd to another directory to ensure we're not inside a Go project.
-        # That'd trigger Go to download the toolchain for that project.
-        cd "$RUNNER_TEMP"
-        # RUNNER_TEMP should be backed by a RAM disk on Windows if
-        # coder/setup-ramdisk-action was used
-        export GOCACHE_DIR="$RUNNER_TEMP""\go-cache"
-        export GOMODCACHE_DIR="$RUNNER_TEMP""\go-mod-cache"
-        export GOPATH_DIR="$RUNNER_TEMP""\go-path"
-        export GOTMP_DIR="$RUNNER_TEMP""\go-tmp"
-        mkdir -p "$GOCACHE_DIR"
-        mkdir -p "$GOMODCACHE_DIR"
-        mkdir -p "$GOPATH_DIR"
-        mkdir -p "$GOTMP_DIR"
-        go env -w GOCACHE="$GOCACHE_DIR"
-        go env -w GOMODCACHE="$GOMODCACHE_DIR"
-        go env -w GOPATH="$GOPATH_DIR"
-        go env -w GOTMPDIR="$GOTMP_DIR"
     - name: Setup Go
       uses: actions/setup-go@0a12ed9d6a96ab950c8f026ed9f722fe0da7ef32 # v5.0.2
       with:
         go-version: ${{ inputs.use-preinstalled-go == 'false' && inputs.version || '' }}
+        cache: ${{ inputs.use-cache }}
 
     - name: Install gotestsum
       shell: bash
       run: go install gotest.tools/gotestsum@0d9599e513d70e5792bb9334869f82f6e8b53d4d # main as of 2025-05-15
 
+    - name: Install mtimehash
+      shell: bash
+      run: go install github.com/slsyy/mtimehash/cmd/mtimehash@a6b5da4ed2c4a40e7b805534b004e9fde7b53ce0 # v1.0.0
+
     # It isn't necessary that we ever do this, but it helps
     # separate the "setup" from the "run" times.
     - name: go mod download