Don't open the commit editor when staging last hunk (#26939)

Closes #26880

Release Notes:

- Removed a behavior where staging the last hunk in the project diff
would open the commit modal.

crates/git_ui/src/project_diff.rs

@@ -806,6 +806,7 @@ impl ProjectDiffToolbar {
     fn project_diff(&self, _: &App) -> Option<Entity<ProjectDiff>> {
         self.project_diff.as_ref()?.upgrade()
     }
+
     fn dispatch_action(&self, action: &dyn Action, window: &mut Window, cx: &mut Context<Self>) {
         if let Some(project_diff) = self.project_diff(cx) {
             project_diff.focus_handle(cx).focus(window);