Refactor repo commit list (#23690)

Refactor repo commit list (#23690)

### Before

* The check of `if PullRequest.BaseRepo.Name` doesn't make sense,
because the `$commitLink` is always constructed below
* Many `if` blocks make the HTML tags (likely) not match in IDE.
Although the rendered result matches, it's very unfriendly to editors or
code analyzer, and it's difficult to read.

### After

Move the `$commitLink` assignment ahead.

Simplify the code, resolve the above problems.