Geo - Clear Gitlab::Geo.proxied_site memoization

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/160479



Merged-by: Michael Kozono <mkozono@gitlab.com>
Approved-by: Michael Kozono <mkozono@gitlab.com>
Co-authored-by: Douglas Barbosa Alexandre <dbalexandre@gmail.com>