ci: add merge commit check to commit linting

.github/workflows/__quality_checks.yml

@@ -79,8 +79,8 @@ jobs:
       - name: Run typecheck 📖
         run: npm run typecheck
 
-  conventional_commits:
-    name: Conventional commits check 💬
+  commits_checks:
+    name: Commit linting 💬✅
     runs-on: ubuntu-latest
 
     steps:
@@ -92,3 +92,8 @@ jobs:
 
       - name: Check if all commits comply with the specification
         uses: webiny/[email protected]
+
+      - name: Check for merge commits
+        run: |
+          git log --merges --oneline | grep -q "^" && exit 1 || exit 0
+

.github/workflows/pull_request.yml

@@ -62,7 +62,7 @@ jobs:
     uses: ./.github/workflows/__quality_checks.yml
     permissions: {}
     with:
-      commit: ${{ github.event.pull_request.head.sha }}
+      commit: ${{ github.event.pull_request.head.ref }}
 
   codeql:
     name: GitHub CodeQL 🔬