chore(ci): serialize auto-merge workflow runs

Author: iamralch

.github/workflows/merge.yml

@@ -4,6 +4,9 @@ on:
   pull_request:
     types: [opened, reopened, labeled]
 
+concurrency:
+  group: ${{ github.workflow }}
+
 jobs:
   merge:
     if: contains(github.event.pull_request.labels.*.name, 'auto-merge')
@@ -18,5 +21,5 @@ jobs:
           GH_TOKEN: ${{ github.token }}
           PR_URL: ${{ github.event.pull_request.html_url }}
         run: |
-          gh pr review --approve --body "LGTM" "$PR_URL"
+          gh pr review --approve "$PR_URL"
           gh pr merge --auto --squash "$PR_URL"