fix: 404 instead of 300 for ambiguous email_or_person

[jennifer-richards]

This changes both the CommunityList family of views and the Person photo view to return a 404 instead of a 300 if the email_or_name in the URL is ambiguous. In both cases, the old approach was attempting to be helpful but assumed that every Person matched had a User whose username could be used as a unique identifier. That is not true, so something needs to be done.

While the 300 response with a list of usernames (or email addresses) is arguably helpful and friendly, I don't think a 404 is wrong - we're just declaring that we don't have a CommunityList or Photo that can be found at that URL. In either context, someone who is bothered by the missing resource is likely to complain about it and we can address the underlying issue.

Fixes #8003

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.91%. Comparing base (c7f6bde) to head (a1f2705).
Report is 103 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8004      +/-   ##
==========================================
+ Coverage   88.78%   88.91%   +0.12%     
==========================================
  Files         296      304       +8     
  Lines       41320    41279      -41     
==========================================
+ Hits        36687    36703      +16     
+ Misses       4633     4576      -57     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[rjsparks]

The line exposing username was incorrect anyhow.
I suspect we'll end up needing to revisit this, likely with person search.