Mergebot should reopen a PR when it's reverted

[ZainRizvi]

Goal
When mergebot reverts a PR, reopen that PR as well. This'll make tracking reverted PRs easier for the authors

Caveat
It appears that sometimes github can't reopen regular PRs. It's been reported this can happen when the branch has been deleted or if it's been "merged" (potentially meaning this feature could only work for ghstack PRs), but this needs more investigation

[malfet]

Sounds simple, let me give it a try...

[malfet]

gh_fetch_url("https://api.github.com/repos/malfet/deleteme/pulls/57", method="PATCH", data={"state":"open"}) is all it takes

[huydhn]

It looks like restoring the deleted branch could be done if there is a need, i.e. pytorch/pytorch#112304 has a restore branch button at the bottom. Although I think it would need to try it out:

• In the case of ghstack, both base and head branches are deleted. So, both needs to be restored
• I couldn't find any GitHub API to do the restore, so we would need to implement the that part ourselves

[malfet]

@huydhn branches are not auto-deleted, and only owner can restore a branch, so if PR is reverted, we should just try to revert as a first step

[malfet]

And it works: malfet/deleteme#58 Cherry-picking PRs into torch