Update JDK version from 17 to 21 in CI workflow

Author: ikseong00

.github/workflows/android-ci.yml

@@ -21,10 +21,10 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: set up JDK 17
+      - name: set up JDK 21
         uses: actions/setup-java@v4
         with:
-          java-version: '17'
+          java-version: '21'
           distribution: 'temurin'
           cache: gradle
 
@@ -54,4 +54,4 @@ jobs:
 #          ./gradlew detekt --continue
 
       - name: Run build
-        run: ./gradlew buildDebug --stacktrace
+        run: ./gradlew buildDebug --stacktrace