500 server error when trying to update a PR that contains conflicts with `rebase`

[qwerty287]

• Gitea version (or commit ref):1.16.0+dev-192-g268b2d0c9
• Git version:2.30.2
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes
  • No
• Logs:

.../api/v1/repo/pull.go:1140:UpdatePullRequest() [E] pull_service.Update: Rebase Error: exit status 1: Whilst Rebasing: <commit hash>
        Rebasing (1/1)\01503derror: could not apply <commit hash>... change README.md
        Resolve all conflicts manually, mark them as resolved with
        "git add/rm <conflicted_files>", then run "git rebase --continue".
        You can instead skip this commit: run "git rebase --skip".
        To abort and get back to the state before "git rebase", run "git rebase --abort".
        Could not apply 5a5fa47... change README.md

        Auto-merging README.md
        CONFLICT (content): Merge conflict in README.md
Completed POST /api/v1/repos/qwerty287/tests/pulls/1/update?style=rebase 500 Internal Server Error in 258.618144ms

Description

If I try to update a PR with conflicts via rebase (using the API), I get a 500 error. If I use the default merge option, I get a 409 Conflict error, which is better. It would be nice if it could return a 409 error if the PR contains conflicts.