Fix: use Gitea-compatible actions

.gitea/workflows/build.yml

@@ -9,19 +9,12 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    container:
+      image: eclipse-temurin:21-jdk
     
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
-
-      - name: Setup Java 21
-        uses: actions/setup-java@v4
-        with:
-          distribution: 'temurin'
-          java-version: '21'
-
-      - name: Setup Gradle
-        uses: gradle/actions/setup-gradle@v3
+        uses: https://gitea.com/actions/checkout@v4
 
       - name: Grant execute permission
         run: chmod +x gradlew
@@ -33,8 +26,7 @@ jobs:
         run: ./gradlew test --no-daemon
 
       - name: Upload artifact
-        uses: actions/upload-artifact@v4
+        uses: https://gitea.com/actions/upload-artifact@v3
         with:
           name: LoChat
           path: build/libs/LoChat-*.jar
-          retention-days: 30