Explain gRPC workflow is non-blocking

Author: jeromegamez

.github/workflows/grpc-tests.yml

@@ -31,6 +31,9 @@ jobs:
   grpc-tests:
     name: gRPC Tests (PHP 8.5)
     runs-on: ubuntu-latest
+    # Non-blocking while the gRPC extension is broken/unstable on PHP 8.5.
+    # See https://github.com/shivammathur/setup-php/issues/1041.
+    # Remove this once upstream releases a stable extension and tests pass.
     continue-on-error: true
     if: ${{ github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository }}