Fix dropdown z index (#12442)

Fixes https://github.com/twentyhq/twenty/issues/11942

This PR creates two different dropdown z indexes, one for normal
dropdowns, and one for the dropdowns inside modals.

packages/twenty-front/src/modules/spreadsheet-import/components/MatchColumnToFieldSelect.tsx

@@ -137,6 +137,7 @@ export const MatchColumnToFieldSelect = ({
         )
       }
       onClickOutside={handleClickOutside}
+      isDropdownInModal
     />
   );
 };