ci: update build settings [forgot that I'm on gradle, not maven 😀] + add cache

Author: lim0sha

.github/workflows/java.yml

@@ -15,5 +15,10 @@ jobs:
         with:
           java-version: '21'
           distribution: 'temurin'
-      - name: Build with Maven
-        run: mvn --batch-mode --update-snapshots package
+          cache: 'gradle'
+
+      - name: Grant execute permission for gradlew
+        run: chmod +x ./gradlew
+
+      - name: Build with Gradle
+        run: ./gradlew build --no-daemon