fix: 修复Windows下subprocess调用失败的问题

在subprocess.check_call()中添加shell=True参数，解决Windows系统下
执行python.exe ensurepip --upgrade时出现CalledProcessError(returncode 2)的问题

- 添加shell=True参数到subprocess调用

Author: linwu

backend/plugin/tools.py

@@ -319,7 +319,7 @@ def install_requirements(plugin: str | None) -> None:
                 pip_install = [sys.executable, '-m', 'pip', 'install', '-r', requirements_file]
                 if settings.PLUGIN_PIP_CHINA:
                     pip_install.extend(['-i', settings.PLUGIN_PIP_INDEX_URL])
-                subprocess.check_call(ensurepip_install, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
+                subprocess.check_call(ensurepip_install, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,shell=True)
                 subprocess.check_call(pip_install, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
             except subprocess.CalledProcessError as e:
                 raise PluginInstallError(f'插件 {plugin} 依赖安装失败：{e}') from e