Upgrade java in GitHub actions

Author: zorgluf

.github/workflows/gradle.yml

@@ -14,10 +14,10 @@ jobs:
     - uses: actions/checkout@v2
     - name: Set env
       run: echo "RELEASE_VERSION=${GITHUB_REF##*/}" >> $GITHUB_ENV
-    - name: Set up JDK 11
+    - name: Set up JDK 21
       uses: actions/setup-java@v1
       with:
-        java-version: '11'
+        java-version: '21'
     - name: Grant execute permission for gradlew
       run: chmod +x gradlew
     - name: Build with Gradle