Problems with oauth2 on login page

[ExplodingDragon]

Description

I added external login credentials idm to gitea and when I log in, the redirect url is wrong. When I manually change the id to idm, I can login normally. Looks like an error introduced by #27798.

# fail
https://git.example.com/user/oauth2/openidConnect
# success
https://git.example.com/user/oauth2/idm

Gitea Version

dev(6035733)

Can you reproduce the bug on the Gitea demo site?

No

Log Gist

No response

Screenshots

No response

Git Version

No response

Operating System

No response

How are you running Gitea?

systemd

Database

None