Unable to migrate repos with duplicate case-different tags

[silverwind]

Description

1. Create new migration from https://github.com/pytorch/pytorch, does not matter whether mirror or not.

After some time, it will error:

2023/07/16 18:19:53 ...ices/task/migrate.go:60:func1() [E] runMigrateTask[6] by DoerID[1] to RepoID[47] for OwnerID[1] failed: SyncRepoBranchesWithRepo: Error 1062 (23000): Duplicate entry '47-update-test-distribute' for key 'UQE_branch_s'
2023/07/16 18:19:53 ...ervices/task/task.go:51:handler() [E] Run task failed: SyncRepoBranchesWithRepo: Error 1062 (23000): Duplicate entry '47-update-test-distribute' for key 'UQE_branch_s'

Likely regression from #22743

Gitea Version

main

Database

mysqld  Ver 11.0.2-MariaDB for osx10.18 on x86_64 (Homebrew)

[wxiaoguang]

This one, but stale:

Convert branch table name column to a new collation for mysql/mssql to support case sensitive because branch names are case sensitive #25623

[silverwind]

Indeed, the repo has two branches with same name but different case:

[wxiaoguang]

There is a workaround in #28131