Use robustcheckout to pull

[marco-c]

In

bugbug/bugbug/repository.py

Line 1521 in 17ac38a

def pull(repo_dir: str, branch: str, revision: str) -> None:

and

bugbug/bugbug/repository.py

Line 1498 in 17ac38a

hg.pull(update=update)

,