ci: add caching for Gradle dependencies in CI workflow

.gitea/workflows/ci.yml

@@ -17,6 +17,15 @@ jobs:
         with:
           distribution: "temurin"
           java-version: "22"
+      - name: "Cache Gradle dependencies"
+        uses: actions/cache@v3
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: gradle-${{ runner.os }}-common
+          restore-keys: |
+            gradle-${{ runner.os }}-
       - name: "Prepare Gradle"
         working-directory: ./backend
         run: gradle clean