Use git config --global user.email for email address in automatic Co-authored-by (#32624)

Release Notes:

- Automatic population of `Co-authored-by` now uses `git config --global
user.email`

---------

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

crates/git_ui/src/commit_modal.rs

@@ -148,6 +148,7 @@ impl CommitModal {
                 }
             }
             git_panel.set_modal_open(true, cx);
+            git_panel.load_local_committer(cx);
         });
 
         let dock = workspace.dock_at_position(git_panel.position(window, cx));