Mastodon login doesn't work (again) with some non-mastodon (but mastodon-compatible) instances

[ielenia]

Are you sure this is not a data issue?

• Yes, this is a Traewelling software bug (not a data issue).

Have you checked for existing issues?

• Yes, I have verified that no existing issue covers this problem.

Affected URL (if any)

No response

Describe the problem

Trying to link a "Mastodon" account will (somewhat inconsistently) give errors, in the same way as described in #1607.

Steps to reproduce

1. Attempt to link a "mastodon" account (in my case ck.catwithaclari.net)
2. It fails with a generic "An error has occurred"

Expected behavior

No response

Environment

Firefox, both mobile and android

Browser console / error messages (optional)

Additional info (optional)

Might be caused by #4692, as I was able to successfully link my "mastodon" account around the time before that would have made its way to release and that is the only change I see since then that seems to have affected Mastodon linking