chore: cache terraform providers between CI test runs (#17373)

Addresses https://github.com/coder/internal/issues/322.

This PR starts caching Terraform providers used by `TestProvision` in
`provisioner/terraform/provision_test.go`. The goal is to improve the
reliability of this test by cutting down on the number of network calls
to external services. It leverages GitHub Actions cache, which [on depot
runners is persisted for 14 days by
default](https://depot.dev/docs/github-actions/overview#cache-retention-policy).

Other than the aforementioned `TestProvision`, I couldn't find any other
tests which depend on external terraform providers.

.github/workflows/ci.yaml

@@ -341,6 +341,12 @@ jobs:
       - name: Setup Terraform
         uses: ./.github/actions/setup-tf
 
+      - name: Download Test Cache
+        id: download-cache
+        uses: ./.github/actions/test-cache/download
+        with:
+          key-prefix: test-go-${{ runner.os }}-${{ runner.arch }}
+
       - name: Test with Mock Database
         id: test
         shell: bash
@@ -365,6 +371,11 @@ jobs:
           gotestsum --junitfile="gotests.xml" --jsonfile="gotests.json" \
             --packages="./..." -- $PARALLEL_FLAG -short -failfast
 
+      - name: Upload Test Cache
+        uses: ./.github/actions/test-cache/upload
+        with:
+          cache-key: ${{ steps.download-cache.outputs.cache-key }}
+
       - name: Upload test stats to Datadog
         timeout-minutes: 1
         continue-on-error: true
@@ -462,6 +473,12 @@ jobs:
         if: runner.os == 'Windows'
         uses: ./.github/actions/setup-imdisk
 
+      - name: Download Test Cache
+        id: download-cache
+        uses: ./.github/actions/test-cache/download
+        with:
+          key-prefix: test-go-pg-${{ runner.os }}-${{ runner.arch }}
+
       - name: Test with PostgreSQL Database
         env:
           POSTGRES_VERSION: "13"
@@ -476,6 +493,11 @@ jobs:
 
           make test-postgres
 
+      - name: Upload Test Cache
+        uses: ./.github/actions/test-cache/upload
+        with:
+          cache-key: ${{ steps.download-cache.outputs.cache-key }}
+
       - name: Upload test stats to Datadog
         timeout-minutes: 1
         continue-on-error: true
@@ -514,6 +536,12 @@ jobs:
       - name: Setup Terraform
         uses: ./.github/actions/setup-tf
 
+      - name: Download Test Cache
+        id: download-cache
+        uses: ./.github/actions/test-cache/download
+        with:
+          key-prefix: test-go-pg-16-${{ runner.os }}-${{ runner.arch }}
+
       - name: Test with PostgreSQL Database
         env:
           POSTGRES_VERSION: "16"
@@ -521,6 +549,11 @@ jobs:
         run: |
           make test-postgres
 
+      - name: Upload Test Cache
+        uses: ./.github/actions/test-cache/upload
+        with:
+          cache-key: ${{ steps.download-cache.outputs.cache-key }}
+
       - name: Upload test stats to Datadog
         timeout-minutes: 1
         continue-on-error: true
@@ -551,6 +584,12 @@ jobs:
       - name: Setup Terraform
         uses: ./.github/actions/setup-tf
 
+      - name: Download Test Cache
+        id: download-cache
+        uses: ./.github/actions/test-cache/download
+        with:
+          key-prefix: test-go-race-${{ runner.os }}-${{ runner.arch }}
+
       # We run race tests with reduced parallelism because they use more CPU and we were finding
       # instances where tests appear to hang for multiple seconds, resulting in flaky tests when
       # short timeouts are used.
@@ -559,6 +598,11 @@ jobs:
         run: |
           gotestsum --junitfile="gotests.xml" -- -race -parallel 4 -p 4 ./...
 
+      - name: Upload Test Cache
+        uses: ./.github/actions/test-cache/upload
+        with:
+          cache-key: ${{ steps.download-cache.outputs.cache-key }}
+
       - name: Upload test stats to Datadog
         timeout-minutes: 1
         continue-on-error: true
@@ -589,6 +633,12 @@ jobs:
       - name: Setup Terraform
         uses: ./.github/actions/setup-tf
 
+      - name: Download Test Cache
+        id: download-cache
+        uses: ./.github/actions/test-cache/download
+        with:
+          key-prefix: test-go-race-pg-${{ runner.os }}-${{ runner.arch }}
+
       # We run race tests with reduced parallelism because they use more CPU and we were finding
       # instances where tests appear to hang for multiple seconds, resulting in flaky tests when
       # short timeouts are used.
@@ -600,6 +650,11 @@ jobs:
           make test-postgres-docker
           DB=ci gotestsum --junitfile="gotests.xml" -- -race -parallel 4 -p 4 ./...
 
+      - name: Upload Test Cache
+        uses: ./.github/actions/test-cache/upload
+        with:
+          cache-key: ${{ steps.download-cache.outputs.cache-key }}
+
       - name: Upload test stats to Datadog
         timeout-minutes: 1
         continue-on-error: true