When a user without a SSO session attempted to access anything in a SAML
group with a query string, previously GitLab would redirect the user
back to original path but drop the query string.

We fixed the redirection originally in
!66791, but
`request.path_info` drops query strings. To ensure the query strings are
passed to the `RelayState`, we need to use `request.fullpath`.

Relates to #338833

Changelog: fixed