我试图在 VS Code IDE 下创建一个新的颤振项目。我安装了颤振扩展，但没有运行任何项目，它在通知中显示运行状态，并显示如下输出。
Unable to 'pub upgrade' flutter tool. Retrying in five seconds... (3 tries left)
Running pub upgrade...
Could not find a file named "pubspec.yaml" in "C:\src\Flutter\.pub-cache\hosted\pub.dartlang.org\analyzer-1.5.0".
Error (66): Unable to 'pub upgrade' flutter tool. Retrying in five seconds... (2 tries left)
Running pub upgrade...
Could not find a file named "pubspec.yaml" in "C:\src\Flutter\.pub-cache\hosted\pub.dartlang.org\analyzer-1.5.0".
Error (66): Unable to 'pub upgrade' flutter tool. Retrying in five seconds... (1 tries left)
Error: 'pub upgrade' still failing after 10 tries.