Revert "Quarantine GitHub OAuth test"

This reverts commit 970576c5.

qa/qa/specs/features/browser_ui/1_manage/login/login_via_oauth_spec.rb

 # frozen_string_literal: true
 
 module QA
-  # https://gitlab.com/gitlab-org/quality/nightly/issues/83
-  context 'Manage', :orchestrated, :oauth, :quarantine do
+  context 'Manage', :orchestrated, :oauth do
     describe 'OAuth login' do
       it 'User logs in to GitLab with GitHub OAuth' do
         Runtime::Browser.visit(:gitlab, Page::Main::Login)