Update ci.yml

Author: LeoAndo

.github/workflows/ci.yml

@@ -19,10 +19,10 @@ jobs:
 
     - uses: actions/checkout@v4
 
-    - name: set up JDK 17
+    - name: set up JDK 21
       uses: actions/setup-java@v3
       with:
-        java-version: '17'
+        java-version: '21'
         distribution: 'temurin'
 
     - name: Create local.properties