Use ubuntu-latest runner label

Align runs-on with the standard Gitea/GitHub-compatible label so
workflows stay portable. The Main label has been replaced by
ubuntu-latest on the registered runner.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -34,8 +34,7 @@ on:
 
 jobs:
   build-release:
-    # 对应 Gitea Runner "Act Runner 1" 的标签
-    runs-on: Main
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout (full history)
         uses: actions/checkout@v4