Conflict detection broken for PRs that have been updated via merge to resolve conflicts #18130
Description
Gitea Version
1.16.0+dev-759-g8ce1b539b
Git Version
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Operating System
No response
How are you running Gitea?
Docker (:dev-rootless) or https://try.gitea.io
Database
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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
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