ci: include workflow in concurrency group (#512)

This hasn't caused problems because we don't have multiple workflows in
our standard Rails setup, but we hit it on other stacks where we do and
there's no downside so might as well do this here as best practice

variants/github_actions_ci/workflows/ci.yml.tt

@@ -6,8 +6,8 @@ on:
       - main
       - production
 concurrency:
-  # Pushing new changes to a branch will cancel any in-progress CI runs
-  group: ${{ github.ref }}
+  # Pushing new changes to a branch will cancel any in-progress CI runs of this workflow
+  group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 env:
   RAILS_ENV: test