The `vim` crate's tests depend on `git_ui`, which transitively depends
on `recent_projects` with `test-support` enabled. This causes
`recent_projects` to include RemoteConnectionOptions::Mock` variant
handling. However, `git_ui` was not enabling its `test-support` feature,
causing compilation failures when the Mock variant was expected but not
available.

This commit enables the `test-support` feature for both `git_ui` and
`title_bar` dev-dependencies in the `vim` crate, ensuring the Mock
variant is consistently available during testing.

Release Notes:

- N/A