Update CI workflow to install Python 3.11 and adjust dependency installation commands

.gitea/workflows/ci.yml

@@ -28,14 +28,16 @@ jobs:
         run: |
           npm run build -- --no-check || true
 
-      - name: 安装 Python
+      - name: 安装 Python 3.11
         run: |
           apt-get update
-          apt-get install -y python3 python3-pip
+          apt-get install -y python3.11 python3.11-venv python3.11-distutils python3-pip
+          update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.11 1
+          python3 --version
 
       - name: 安装后端依赖
         working-directory: back
-        run: pip3 install --break-system-packages -i https://pypi.tuna.tsinghua.edu.cn/simple -r requirements.txt
+        run: python3.11 -m pip install --break-system-packages -i https://pypi.tuna.tsinghua.edu.cn/simple -r requirements.txt
 
       - name: 构建 Docker 镜像
         run: docker-compose build