bumped maven.yml to use checkout@v4

Author: lpandzic

.github/workflows/maven.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Set up JDK 17
         uses: actions/setup-java@v1
         with: