update workflow to java 21

.github/workflows/gradle.yml

@@ -18,10 +18,10 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v4
         with:
-          java-version: '17'
+          java-version: '21'
           distribution: 'temurin'
       - name: Build project with gradle
         uses: gradle/actions/setup-gradle@v4