Conflict detection broken for PRs that have been updated via merge to resolve conflicts

[CirnoT]

Gitea Version

1.16.0+dev-759-g8ce1b539b

Git Version

No response

Operating System

No response

How are you running Gitea?

Docker (:dev-rootless) or https://try.gitea.io

Database

No response

Can you reproduce the bug on the Gitea demo site?

Yes

Log Gist

No response

Description

Exists since #18004 was merged (so since f1e8562; last working is 9296baf).

Simplest example can be seen on https://try.gitea.io/Yumaa/kanna/pulls/1

Screenshots

No response

[lunny]

Maybe @zeripath can help.