upgrade the checkout action

Author: pschichtel

.github/workflows/maven.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up JDK
       uses: actions/setup-java@v3
       with: