Setting build to Java 21.

Author: a2geek

.github/workflows/gradle.yml

@@ -23,10 +23,10 @@ jobs:
 
     steps:
     - uses: actions/checkout@v3
-    - name: Set up JDK 11
+    - name: Set up JDK 21
       uses: actions/setup-java@v3
       with:
-        java-version: '11'
+        java-version: '21'
         distribution: 'temurin'
     - name: Setup Gradle
       uses: gradle/actions/setup-gradle@v4