Fix some bugs with editor: diff clipboard with selection (#34999)

Improves testing around `editor: diff clipboard with selection` as well.

Release Notes:

- Fixed some bugs with `editor: diff clipboard with selection`

crates/editor/src/editor_tests.rs

@@ -16864,7 +16864,7 @@ async fn test_multibuffer_reverts(cx: &mut TestAppContext) {
 }
 
 #[gpui::test]
-async fn test_mutlibuffer_in_navigation_history(cx: &mut TestAppContext) {
+async fn test_multibuffer_in_navigation_history(cx: &mut TestAppContext) {
     init_test(cx, |_| {});
 
     let cols = 4;