Add branch to git panel (#24485)

This PR adds the branch selector to the git panel and fixes a few bugs
in the repository selector.

Release Notes:

- N/A

---------

Co-authored-by: ConradIrwin <conrad.irwin@gmail.com>
Co-authored-by: Conrad <conrad@zed.dev>

crates/git_ui/src/repository_selector.rs

@@ -34,6 +34,7 @@ impl RepositorySelector {
         let picker = cx.new(|cx| {
             Picker::nonsearchable_uniform_list(delegate, window, cx)
                 .max_height(Some(rems(20.).into()))
+                .width(rems(15.))
         });
 
         let _subscriptions =