build: add commit message linting to workflow

Run linting on the commit message of the first commit in a pull
request as part of our GitHub actions CI workflow. If linting fails
the pull request will be labelled as requiring a fix to the commit
message. The check itself will always pass so as to not concern
first time contributors.

Signed-off-by: Richard Lau <[email protected]>

Author: richardlau

.github/workflows/CI.yml

@@ -49,6 +49,23 @@ jobs:
         node-version: 10.x
     - name: Lint addon docs
       run: NODE=$(which node) make lint-addon-docs
+  lint-commit-message:
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: Lints message of the first commit in this pull request
+        continue-on-error: true
+        run: bash -x tools/lint-pr-commit-message.sh ${{ github.event.number }} || echo ::set-env name=needs_fixup::true
+      - name: Label on commit message lint failure
+        if: env.needs_fixup == 'true'
+        uses: actions/[email protected]
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          args: label "needs commit message fix"
   lint-cpp:
     runs-on: ubuntu-latest
     steps: