Update migration_guides/70.x.x-to-71.0.0-migration-guide.md

Co-authored-by: rmccar <[email protected]>

migration_guides/70.x.x-to-71.0.0-migration-guide.md

@@ -111,7 +111,7 @@ This section will list the changes that will impact more than one component
 
 [**Link to PR**](https://github.com/ONSdigital/design-system/pull/3285)
 
--   **Description of change:** Font size classes have been updated to reflect the new size naming convention in the Design System. This update replaces the old naming convention (e.g., xxxl, xxl) with a numerical system (e.g., 3xl, 2xl), similar to the one used for padding and margins.
+-   **Description of change:** Font size classes have been updated to reflect the new size naming convention. This change replaces the old naming convention (e.g., xxxl, xxl) with a numerical system (e.g., 3xl, 2xl), the same as the one that has been brought for padding and margins.
 
 -   **Reason for change:** This update standardises how sizes are referenced across the system.