Add Java 21 github action

.github/workflows/java-21.yml

@@ -0,0 +1,41 @@
+# This workflow will build a Java project with Gradle
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-java-with-gradle
+
+name: Java 21
+
+on:
+  push:
+    branches: [ 3.2.*, 3.1.* ]
+  pull_request:
+    branches: [ 3.2.*, 3.1.* ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest            
+    name: Java 21 build
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up JDK 21
+        uses: actions/setup-java@v3
+        with:
+          java-version: 21
+          distribution: liberica          
+      - name: Cache Gradle packages
+        uses: actions/cache@v3
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle*', '**/gradle-wrapper.properties') }}
+          restore-keys: |
+            ${{ runner.os }}-gradle-
+      - name: Validate Gradle wrapper
+        uses: gradle/wrapper-validation-action@v1
+      - name: Build with Gradle
+        run: ./gradlew build
+      - name: Cleanup Gradle Cache
+        # Remove some files from the Gradle cache, so they aren't cached by GitHub Actions.
+        # Restoring these files from a GitHub Actions cache might cause problems for future builds.
+        run: |
+          rm -f ~/.gradle/caches/modules-2/modules-2.lock
+          rm -f ~/.gradle/caches/modules-2/gc.properties