Surface 'always' in notification about incoming changes to a PR

Re https://github.com/microsoft/vscode-pull-request-github/issues/3711#issuecomment-1218027233, it would be nice if the option to always pull was an action in this notification: ![image](https://user-images.githubusercontent.com/30305945/186527817-48cacec6-18af-4911-9070-d45e702bcfeb.png)