Initial fix of the z-index

Co-Authored-By: Antonio Scandurra <antonio@zed.dev>
Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/workspace2/src/toolbar.rs

@@ -105,6 +105,8 @@ impl Render for Toolbar {
         v_stack()
             .p_1()
             .gap_2()
+            // todo!() use a proper constant here (ask Marshall & Nate)
+            .z_index(80)
             .border_b()
             .border_color(cx.theme().colors().border_variant)
             .bg(cx.theme().colors().toolbar_background)