perf(ci): 构建任务放宽Runner标签到saas，利用新CI服务器资源

将build-staging和build-production的runs-on从 saas+build-farm
放宽为 saas，让新CI服务器的6个build-only Runner也能承接构建任务，
解决三镜像并行构建时的资源竞争问题。

.gitea/workflows/ci-cd.yml

@@ -408,9 +408,7 @@ jobs:
         '
   build-staging:
     name: Build Staging ${{ matrix.service_display }} Image
-    runs-on:
-    - saas
-    - build-farm
+    runs-on: saas
     timeout-minutes: ${{ matrix.timeout }}
     needs:
     - validate
@@ -684,9 +682,7 @@ jobs:
         '
   build-production:
     name: Build Production ${{ matrix.service_display }} Image
-    runs-on:
-    - saas
-    - build-farm
+    runs-on: saas
     timeout-minutes: ${{ matrix.timeout }}
     needs:
     if: startsWith(github.ref, 'refs/tags/v')