Check out pull request by number should show PRs in picker

[bpasero]

Testing #3144

I would have expected to see a list of PRs to pick from in the picker.

In fact, I would not even name this feature "...by number" but just "Checkout Pull Request..." and from the picker allow to type anything including the number.

[enricodias]

allow to type anything

Being able to type the full PR url would be especially useful.