build: "Quick Checks" runs consistency checks concurrently with others

Originally we had this running as part of the Unit Tests job because most
of the checks are relatively fast. However, the addition of the protobuf
generation check made that no longer be true because it needs to download
and run protoc.

With that extra overhead it now _is_ productive to spend the time booting
and installing Go on third worker, as long as GitHub Actions continues
to let us run all three of these jobs concurrently most of the time.

.github/workflows/checks.yml

@@ -42,8 +42,9 @@ jobs:
         with:
           go-version: ${{ steps.go.outputs.version }}
 
-      # NOTE: This cache is shared with the e2e-tests job, so the corresponding
-      # step in that job must always be identical to this one.
+      # NOTE: This cache is shared so the following step must always be
+      # identical across the unit-tests, e2e-tests, and consistency-checks
+      # jobs, or else weird things could happen.
       - name: Cache Go modules
         uses: actions/cache@v3
         with:
@@ -52,31 +53,10 @@ jobs:
           restore-keys: |
             go-mod-
 
-      - name: "go.mod and go.sum consistency check"
-        run: |
-          go mod tidy
-          if [[ -n "$(git status --porcelain)" ]]; then
-            echo "go.mod/go.sum are not up-to-date. Run 'go mod tidy' and then commit the updated files."
-            exit 1
-          fi
-
       - name: "Unit tests"
         run: |
           go test ./...
 
-      # We'll also deal with some general consistency/lint/style checks
-      # here just because they are relatively fast and so not worth running
-      # concurrently given the cost of _yet again_ installing Go and checking
-      # out the source code in another worker.
-      - name: "Code consistency checks"
-        run: |
-          make fmtcheck generate staticcheck exhaustive protobuf
-          if [[ -n "$(git status --porcelain)" ]]; then
-            echo "Generated files are inconsistent. Run 'make generate' and 'make protobuf' locally and then commit the updated files."
-            git status --porcelain
-            exit 1
-          fi
-
   e2e-tests:
     # This is an intentionally-limited form of our E2E test run which only
     # covers Terraform running on Linux. The build.yml workflow runs these
@@ -98,8 +78,9 @@ jobs:
         with:
           go-version: ${{ steps.go.outputs.version }}
 
-      # NOTE: This cache is shared with the e2e-tests job, so the corresponding
-      # step in that job must always be identical to this one.
+      # NOTE: This cache is shared so the following step must always be
+      # identical across the unit-tests, e2e-tests, and consistency-checks
+      # jobs, or else weird things could happen.
       - name: Cache Go modules
         uses: actions/cache@v3
         with:
@@ -111,3 +92,48 @@ jobs:
       - name: "End-to-end tests"
         run: |
           TF_ACC=1 go test -v ./internal/command/e2etest
+
+  consistency-checks:
+    name: "Code Consistency Checks"
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: "Fetch source code"
+        uses: actions/checkout@v2
+
+      - name: Determine Go version
+        id: go
+        uses: ./.github/actions/go-version
+
+      - name: Install Go toolchain
+        uses: actions/setup-go@v2
+        with:
+          go-version: ${{ steps.go.outputs.version }}
+
+      # NOTE: This cache is shared so the following step must always be
+      # identical across the unit-tests, e2e-tests, and consistency-checks
+      # jobs, or else weird things could happen.
+      - name: Cache Go modules
+        uses: actions/cache@v3
+        with:
+          path: "~/go/pkg"
+          key: go-mod-${{ hashFiles('go.sum') }}
+          restore-keys: |
+            go-mod-
+
+      - name: "go.mod and go.sum consistency check"
+        run: |
+          go mod tidy
+          if [[ -n "$(git status --porcelain)" ]]; then
+            echo >&2 "ERROR: go.mod/go.sum are not up-to-date. Run 'go mod tidy' and then commit the updated files."
+            exit 1
+          fi
+
+      - name: "Code consistency checks"
+        run: |
+          make fmtcheck generate staticcheck exhaustive protobuf
+          if [[ -n "$(git status --porcelain)" ]]; then
+            echo >&2 "ERROR: Generated files are inconsistent. Run 'make generate' and 'make protobuf' locally and then commit the updated files."
+            git >&2 status --porcelain
+            exit 1
+          fi