can't unapprove my own PRs

[matthiaskrgr]

People need to be able to r- their own PRs.

Use case:

I make a PR that updates clippy.
The PR is r+ed and prioritized.
In the meantime another rollup merges and breaks clippy again.
Now the clippy-pr needs to be updated again to a working version of clippy since it won't pass CI otherwise but I cannot prevent it from being tested and potentially waste 3 hours of CI time since I cannot r- PRs I authored.

rust-lang/rust#61298 (comment)

[kennytm]

Note that you could workaround by close-and-reopen or push a new commit.