[Feature request] Update/delete Carson's message when base branch has been fixed

[Kocal]

Follows #209.

When fixing the base branch in the PR template, it would be nice to see an update from Carson, update or delete its message for two reasons:

1. to confirm that you fixed the base branch
2. to reduce the noise, an automated-comment telling about a fixed issue is not really useful I think

WDYT?

[weaverryan]

Makes sense to me!

[OskarStark]

I manually mark the comment as outdated sometimes