Bring back PR automatic outdated commit check pre-emption (#8145)

* Bring back PR automatic outdated commit check pre-emption

* Trigger a re-run

.github/workflows/run-build-and-acceptance-tests.yml

@@ -12,6 +12,18 @@ env:
   PULUMI_TEST_OWNER: "moolumi"
   PR_COMMIT_SHA: ${{ github.event.client_payload.pull_request.head.sha }}
 
+# Cancel checks on prior commits when new commits are added to a PR.
+# This is motivated by temporary throughput issues on our GitHub
+# Actions workers availability.
+#
+# Note from GitHub docs: Concurrency is currently in beta and subject
+# to change.
+#
+# See also: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency
+concurrency:
+  group: run-build-acceptance-tests-${{ github.ref }}-${{ github.head_ref }}
+  cancel-in-progress: true
+
 jobs:
   comment-notification:
     # We only care about adding the result to the PR if it's a repository_dispatch event
@@ -50,6 +62,10 @@ jobs:
     name: Lint SDKs
     runs-on: ubuntu-latest
     steps:
+      - name: debug ref vs head_ref 2
+        run: |
+          echo "github.ref      = ${{ github.ref }}"
+          echo "github.head_ref = ${{ github.head_ref }}"
       - name: Set up Go ${{ matrix.go-version }}
         uses: actions/setup-go@v1
         with: