Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/maven.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
     - name: Set up JDK 1.8
       uses: actions/setup-java@v2
       with: