GHA: Update upload-artifact to v4

https://github.blog/changelog/2024-02-13-deprecation-notice-v1-and-v2-of-the-artifact-actions/

.github/workflows/maven.yml

@@ -27,7 +27,7 @@ jobs:
           restore-keys: ${{ runner.os }}-m2
       - name: Build with Maven
         run: mvn -B package --file pom.xml
-      - uses: actions/upload-artifact@v2
+      - uses: actions/upload-artifact@v4
         with:
           name: jar
           path: target/*.jar