[Validation] Error count not updated after save

Reproduction path:
Open document in visual editing
Create e.g. 3 validation errors
See banner saying 'This document contains 3 error'
Fix document to not have any errors and save document
Banner saying 'This document contains 3 error' is still shown since this is still part of the response

In addition, text should be updated to say 'This document contains 3 errors', instead of 'This document contains 3 error'.