Open PR from external link: Needs confirmation dialog

[aeschli]

Testing microsoft/vscode#274805

• clone https://github.com/microsoft/vscode-css-languageservice.git and open in VS Code on main

• Open vscode-insiders://github.vscode-pull-request-github/checkout-pull-request?%7B%22owner%22%3A%22microsoft%22%2C%22repo%22%3A%22vscode-css-languageservice%22%2C%22pullRequestNumber%22%3A460%7D as external link
  -this checks out the PR with out any user consent

It needs something like this: