Run only one acceptance job at a time (#1032)

See https://docs.github.com/en/actions/using-jobs/using-concurrency

Author: nfx

.github/workflows/acceptance.yml

@@ -9,6 +9,9 @@ permissions:
   contents: read
   pull-requests: write
 
+concurrency:
+  group: single-acceptance-job-per-repo
+
 jobs:
   integration:
     if: github.event_name == 'pull_request' && github.event.pull_request.draft == false