Merge branch '508720-handle-404s' into 'master'

Handle 404s when fetching GitHub user details

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/175795



Merged-by: James Nutt <jnutt@gitlab.com>
Approved-by: James Nutt <jnutt@gitlab.com>
Co-authored-by: Luke Duncalfe <lduncalfe@eml.cc>