ci: grant exec permission to gradlew

.github/workflows/build.yml

@@ -14,12 +14,15 @@ jobs:
       - name: Check out repository
         uses: actions/checkout@v4
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v4
         with:
           distribution: 'adopt'
           java-version: '21'
 
+      - name: Grant execution permission to Gradle Wrapper
+        run: chmod +x gradlew
+
       - name: Build with Gradle
         run: ./gradlew assembleDebug