Build/Test Tools: Include the commit short summary in Slack messages.

This gives more context to GitHub Action related Slack messages without the need to click the workflow URL, or unfurl the links (which shows lots of unnecessary information, such as the repository description and image).

Props earnjam.
See #52644.

git-svn-id: https://develop.svn.wordpress.org/trunk@51647 602fd350-edb4-49c9-b593-d223f7449a82

.github/workflows/slack-notifications.yml

@@ -60,9 +60,18 @@ jobs:
         id: previous-conclusion
         run: echo "::set-output name=previous_conclusion::${{ steps.previous-result.outputs.result }}"
 
+      - name: Prepare commit message.
+        id: commit-message
+        run: |
+          COMMIT_MESSAGE=$(cat <<'EOF' | awk 'NR==1' | sed 's/\"/\\"/g'
+          ${{ github.event.workflow_run.head_commit.message }}
+          EOF
+          )
+          echo "::set-output name=commit_message_escaped::${COMMIT_MESSAGE}"
+
       - name: Construct payload and store as an output
         id: create-payload
-        run: echo "::set-output name=payload::{\"workflow_name\":\"${{ github.event.workflow_run.name }}\",\"ref_name\":\"${{ github.event.workflow_run.head_branch }}\",\"run_url\":\"${{ github.event.workflow_run.html_url }}\"}"
+        run: echo "::set-output name=payload::{\"workflow_name\":\"${{ github.event.workflow_run.name }}\",\"ref_name\":\"${{ github.event.workflow_run.head_branch }}\",\"run_url\":\"${{ github.event.workflow_run.html_url }}\",\"commit_message\":\"${{ steps.commit-message.outputs.commit_message_escaped }}\"}"
 
   # Posts notifications when a workflow fails.
   failure: