Fix duplicate accounts being created when fetching an account for its key only (...

Fix duplicate accounts being created when fetching an account for its key only (#13147)

Fixes #13136

When a user's canonical acct domain is different from its id's domain
(WEB_DOMAIN ≠ LOCAL_DOMAIN), two webfinger queries are required to find the
canonical domain from the URI. However, we skip webfinger queries when
updating only the key of a remote user, which led to the creation of a
duplicate account, using the URI's domain instead of the canonical acct: one.