Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/maven-compiler.yml

@@ -22,7 +22,7 @@ jobs:
 
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v6
     - name: Set up JDK 1.8
       uses: actions/setup-java@v2
       with: