Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/maven.yml

@@ -4,9 +4,9 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v1
+    - uses: actions/checkout@v4
     - name: GitHub Actions for Apache Maven
-      uses: actions/checkout@v1
+      uses: actions/checkout@v4
     - run: |
         mvn clean install
         mvn test