fix(ci): 修复 tests.yml - 移除不存在的 Docker 镜像，改用主机运行

- runs-on 改为 runtime-builder（匹配 runner labels）
- 移除 container: xiaoxia-ci-python:3.12（镜像不存在）
- Python 依赖在步骤中直接安装

.gitea/workflows/tests.yml

@@ -8,9 +8,7 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
-    container:
-      image: xiaoxia-ci-python:3.12
+    runs-on: runtime-builder
 
     steps:
     - name: Checkout code
@@ -61,9 +59,7 @@ jobs:
         PYTHONPATH="$PWD/apps/api:$PWD" python -m pytest tests/unit -q
 
   lint:
-    runs-on: ubuntu-latest
-    container:
-      image: xiaoxia-ci-python:3.12
+    runs-on: runtime-builder
 
     steps:
     - name: Checkout code