Description

Snackbar notices don't seem to be working in the Library.

There is code to trigger a notification, for example when deleting a pattern, but the notice doesn't appear in the UI.

Step-by-step reproduction instructions

1. Open the site editor
2. Open the library from the navigation menu.
3. Open the 'Custom patterns' from the navigation menu
4. Using the 'Actions' dropdown or the delete shortcut, try deleting a pattern

Expected: The pattern is deleted, a snackbar notice is shown confirming, and the deletion is announced to screenreaders.
Actual: The pattern is deleted, there's no snackbar or announcement

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes