CI: update PR branch testing instructions on merge (#1211)

.github/workflows/pr-commenter.yml → .github/workflows/node-branch-exec.yml

@@ -1,4 +1,4 @@
-name: Pull Request Commenter
+name: Node.js Branch Exec
 
 on:
   # pull_request_target required for pull-requests:write permission on fork PRs
@@ -8,6 +8,7 @@ on:
       - opened
       - reopened
       - synchronize  # PR's branch was edited (i.e. new commits)
+      - closed
     paths:
       - '*'
       - 'src/**'
@@ -19,6 +20,7 @@ concurrency:
 
 jobs:
   npm-exec-test:
+    if: github.event.action != 'closed'
     runs-on: ${{ matrix.os }}-latest
     strategy:
       matrix:
@@ -31,8 +33,11 @@ jobs:
         run: npm exec --loglevel verbose --yes -- "github:${{ github.event.pull_request.head.repo.full_name }}#${HEAD_REF}" --help
 
   npm-exec:
+    if: github.event.action != 'closed'
     needs:
       - npm-exec-test
+    permissions:
+      pull-requests: write
     runs-on: ubuntu-latest
     steps:
       - uses: thollander/actions-comment-pull-request@v2
@@ -45,3 +50,21 @@ jobs:
             ```
             _Comment generated by the [${{ github.workflow }}](https://github.com/${{ github.repository }}/actions/runs/${{ github.run_id }}/attempts/${{ github.run_attempt }}) workflow._
           comment_tag: npm-exec
+
+  npm-exec-comment-update:
+    if: github.event.action == 'closed' && github.event.pull_request.merged
+    permissions:
+      pull-requests: write
+    runs-on: ubuntu-latest
+    steps:
+      - uses: thollander/actions-comment-pull-request@v2
+        with:
+          message: |
+            ## :test_tube: Branch testing instructions
+            This pull request has been merged, its base branch can be tested locally with the following command:
+            ```shell
+            npm exec --yes -- "github:${{ github.event.pull_request.base.repo.full_name }}#${{ github.event.pull_request.base.ref }}" [commands..] [options]
+            ```
+            _Comment generated by the [${{ github.workflow }}](https://github.com/${{ github.repository }}/actions/runs/${{ github.run_id }}/attempts/${{ github.run_attempt }}) workflow._
+          comment_tag: npm-exec
+          mode: recreate