Update GitHub actions to use actions/cache@v4

https://github.blog/changelog/2024-12-05-notice-of-upcoming-releases-and-breaking-changes-for-github-actions/#actions-cache-v1-v2-and-actions-toolkit-cache-package-closing-down

Thanks to Sebastian Nagel for the heads up.

Author: ato

.github/workflows/maven.yml

@@ -22,7 +22,7 @@ jobs:
         java-version: ${{ matrix.jdk }}
         distribution: 'temurin'
     - name: Cache local Maven repository
-      uses: actions/cache@v2
+      uses: actions/cache@v4
       with:
         path: ~/.m2/repository
         key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}