chore: update GitHub Actions to v4

Update deprecated v2 actions to current v4 versions to avoid Node.js deprecation warnings

Author: samfert

.github/workflows/gradle.yml

@@ -16,13 +16,13 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
     - name: Set up JDK 11
-      uses: actions/setup-java@v2
+      uses: actions/setup-java@v4
       with:
         distribution: zulu
         java-version: '11'
-    - uses: actions/cache@v2
+    - uses: actions/cache@v4
       with:
         path: |
           ~/.gradle/caches