[meta] changelog CI check sometimes doesn't run

[shiftinv]

^{(originally part of #819)}

The changelog workflow sometimes(?) just doesn't run after creating a PR, it gets stuck in "expected" indefinitely.

Due to the concurrency rules only one instance of that job should run at a time, with the other ones automatically being canceled. However it seems like they're cancelling each other, resulting in not a single one running to completion.

I believe this worked fine for a while and only started happening recently, which might indicate a GitHub bug or edge case, no clue.

[onerandomusername]

Ideally we should also report a pending status for changelog rather than a failed status, as it otherwise marks every commit as failed