Fix: PR builder check out src (iluwatar#2431)

Author: iluwatar

.github/workflows/maven-pr-builder.yml

@@ -40,6 +40,7 @@ jobs:
 
     - name: Checkout Code
       uses: actions/checkout@v3
+        ref: ${{ github.event.pull_request.head.sha }}
 
     - name: Set up JDK 17
       uses: actions/setup-java@v3