GitHubCI: add a job to check commitlint status for PRs

Taken from conventional-changelog/commitlint#2568

.github/workflows/commitlint.yml

@@ -0,0 +1,23 @@
+name: commitlint check
+
+on: pull_request
+
+jobs:
+  commitlint:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: Setup Node
+        uses: actions/setup-node@v2
+        with:
+          node-version: 14.x
+      - name: Install dependencies
+        run: npm install
+      - name: Validate all commits from PR
+        run: >
+          for commit in $(git rev-list ${{ github.base_ref }}..${{
+          github.head_ref }}); do
+              npx commitlint --from $commit --to HEAD --verbose
+          done