Fix Gitea CI: add JDK setup, drop unsupported cache action

.github/workflows/build.yml

@@ -15,13 +15,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v2
 
-      - name: Cache dependencies
-        uses: actions/cache@v2
+      - name: Set up JDK
+        uses: actions/setup-java@v4
         with:
-          path: ~/.m2/repository
-          key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
-          restore-keys: |
-            ${{ runner.os }}-maven-
+          distribution: temurin
+          java-version: '11'
 
       - name: Build, test, package
         run: ./mvnw -B package --file pom.xml