Add typo detection to CI (#4107)

Adding the typos crate to our CI will take some doing, as we have
several tests which rely on typos in various ways (e.g. checking state
as the user types), but I thought I'd take a first stab at fixing what
it finds.

Release Notes:

- N/A

crates/search/src/history.rs

@@ -85,7 +85,7 @@ mod tests {
         assert_eq!(
             search_history.current(),
             None,
-            "No current selection should be set fo the default search history"
+            "No current selection should be set for the default search history"
         );
 
         search_history.add("rust".to_string());

crates/search/src/project_search.rs

@@ -2700,7 +2700,7 @@ pub mod tests {
                     );
                     assert!(
                         search_view_2.query_editor.focus_handle(cx).is_focused(cx),
-                        "Focus should be moved into query editor fo the new window"
+                        "Focus should be moved into query editor of the new window"
                     );
                 });
         }).unwrap();