Quarantine admin_sees_user_spec.rb

What does this MR do and why?

Sunday 2024-06-02 12:45 UTC - `gitlab-org/gitla... (gitlab-org/quality/engineering-productivity/master-broken-incidents#6678 - closed) indicated a master broken. The spec in question has been slow for sometime (see Job timeout risk: spec/features/admin/users/adm... (#441334)) but we also merged tailwind related changes recently (see [CSS utilities TG] Overflow wrap > Migrate to T... (#456628 - closed)). Quarantining this spec to test/unblock the builds while we get a chance to invesitgate.

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