[lib] Discard keyserver usernames for updateUserAvatarActionTypes

Summary: issue: ENG-8365

Test Plan: Tested that for updateUserAvatarActionTypes if the user was in the store the username is not changed. Assuming some correctness based on having tested other diffs in this stack

Reviewers: tomek, kamil

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12514