Update workflow java 21

Author: sengthaite

.github/workflows/flutter_ci_cd.yml

@@ -18,7 +18,7 @@ jobs:
         uses: actions/setup-java@v3
         with:
           distribution: 'temurin'
-          java-version: '17'
+          java-version: '21'
 
       - name: Set up Flutter
         uses: subosito/flutter-action@v2