git: Fix git panel not using default width (#26220)

Closes #26062

Removing the width here causes zed to use the default value (inside
default settings) after restart like other panels.

Release Notes:

- Fixed issue where git panel wasn't using default width after restart

Co-authored-by: Mikayla Maki <mikayla@zed.dev>

crates/git_ui/src/git_panel.rs

@@ -374,7 +374,7 @@ impl GitPanel {
             tracked_count: 0,
             tracked_staged_count: 0,
             update_visible_entries_task: Task::ready(()),
-            width: Some(px(360.)),
+            width: None,
             context_menu: None,
             workspace,
             modal_open: false,