x/build/cmd/releasebot: may select wrong current milestone if there are duplicates

[dmitshur]

Releasebot looks for the release milestone for the current release, and uses it for various things during the release process.

GitHub allows for multiple milestones to have the same title that differ only in case. If a duplicate open milestone exists (this may happen, for example, if a duplicate milestone is created accidentally), releasebot currently may pick the wrong milestone, which negatively impacts its behavior.

I'll send a CL to update releasebot to look for duplicate open milestones, and report it as a fatal problem if so (since humans will need to figure out how to deal with it), like so:

cannot find the GitHub milestone for release go1.18beta1: found closed or duplicate milestones:
	• open milestone "go1.18" (https://github.com/golang/go/milestone/241)
	• open milestone "Go1.18" (https://github.com/golang/go/milestone/201)
exit status 1

I'll also close (and after some time passes, delete) the empty second "go1.18" milestone that I understand was created accidentally. (Not to be confused with the real Go1.18 milestone.)

CC @golang/release, @cherrymui.

[gopherbot]

Change https://golang.org/cl/372534 mentions this issue: cmd/releasebot: ensure no duplicate release milestones exist