chore: use Cow instead of String for tooltips (#2838)

A QoL change to align `Tooltip` with other elements like `Label`
Release Notes:

- N/A

crates/workspace/src/toolbar.rs

@@ -220,7 +220,7 @@ fn nav_button<A: Action, F: 'static + Fn(&mut Toolbar, &mut ViewContext<Toolbar>
     spacing: f32,
     on_click: F,
     tooltip_action: A,
-    action_name: &str,
+    action_name: &'static str,
     cx: &mut ViewContext<Toolbar>,
 ) -> AnyElement<Toolbar> {
     MouseEventHandler::<A, _>::new(0, cx, |state, _| {
@@ -252,7 +252,7 @@ fn nav_button<A: Action, F: 'static + Fn(&mut Toolbar, &mut ViewContext<Toolbar>
     })
     .with_tooltip::<A>(
         0,
-        action_name.to_string(),
+        action_name,
         Some(Box::new(tooltip_action)),
         tooltip_style,
         cx,