Major changes:
1. do not sync ".keep" file during tests
2. fix incorrect route handler and empty repo handling (backported as #33253 with tests)
3. do not use `RepoRef`: most of the calls are abuses.
4. Use `git.RefType` instead of a new type definition `RepoRefType` on `context`.
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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>