Update CI Java version

Author: randomnetcat

.github/workflows/ci.yml

@@ -15,10 +15,10 @@ jobs:
         with:
           submodules: "recursive"
 
-      - name: Set up JDK 1.13
+      - name: Set up Java
         uses: actions/setup-java@v1
         with:
-          java-version: 1.13
+          java-version: 1.21
 
       - name: Grant execute permission for gradlew
         run: chmod +x gradlew