build: fix commit linter on unrebased PRs

.github/workflows/commit-lint.yml

@@ -2,19 +2,24 @@ name: "Commit messages adheres to guidelines at https://goo.gl/p2fr5Q"
 
 on: [pull_request]
 
+env:
+  NODE_VERSION: 14.x
+
 jobs:
   lint-commit-message:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
         with:
           ref: ${{ github.event.pull_request.head.sha }}
-          # Last 100 commits should be enough for a PR
-          fetch-depth: 100
-      - name: Use Node.js 12
-        uses: actions/setup-node@v1
+          fetch-depth: ${{ github.event.pull_request.commits }} + 1
+      - name: Download problem matcher from HEAD
+        # This is needed for PR that have not been rebased.
+        run: curl -L https://github.com/nodejs/node/raw/HEAD/.github/workflows/commit-lint-problem-matcher.json > .github/workflows/commit-lint-problem-matcher.json
+      - name: Use Node.js ${{ env.NODE_VERSION }}
+        uses: actions/setup-node@v2
         with:
-          node-version: 12.x
+          node-version: ${{ env.NODE_VERSION }}
       - name: Validate commit messages
         run: |
           echo "::add-matcher::.github/workflows/commit-lint-problem-matcher.json"