Update Github actions to use JDK 21

Author: AmrDeveloper

.github/workflows/build.yml

@@ -25,7 +25,7 @@ jobs:
       - name: Set Up JDK
         uses: actions/setup-java@v4
         with:
-          java-version: '17'
+          java-version: '21'
 
       - name: Run Tests
         run: ./gradlew test