ci: upgrade actions/checkout@v4 in github actions

Author: javier-godoy

.github/workflows/maven.yml

@@ -18,7 +18,7 @@ jobs:
   build-vaadin14:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up JDK
       uses: actions/setup-java@v3
       with: