Update build.yml

Author: hykilpikonna

.github/workflows/build.yml

@@ -13,11 +13,11 @@ jobs:
       - name: Check out code
         uses: actions/checkout@v3
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v3
         with:
           distribution: temurin
-          java-version: '17'
+          java-version: '21'
 
       - name: Grant Gradle permissions
         run: chmod +x gradlew