Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/maven.yml

@@ -8,7 +8,7 @@ jobs:
     name: Java 21 test build
     steps:
     - name: "Check out code"
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: "Set up JDK"
       uses: actions/setup-java@v5
       with:

.github/workflows/release.yml

@@ -14,7 +14,7 @@ jobs:
       contents: write
     steps:
       - name: "check out code"
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: "set up JDK"
         uses: actions/setup-java@v4