[identity] make sure we don't call refresh keys task twice when fetching content and notif keys

Summary: check if we've already called the task so that we don't call it twice

Test Plan: confirmed with logs that the task is only called once now when fetching content/notif otks

Reviewers: bartek

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11677