Merge branch 'sh-fix-oauth2-callback-caps' into 'master'

Downcase aliased OAuth2 callback providers

Closes #57156

See merge request gitlab-org/gitlab-ce!24877

changelogs/unreleased/sh-fix-oauth2-callback-caps.yml

+---
+title: Downcase aliased OAuth2 callback providers
+merge_request: 24877
+author:
+type: fixed

config/routes/import.rb

 # Alias import callbacks under the /users/auth endpoint so that
 # the OAuth2 callback URL can be restricted under http://example.com/users/auth
 # instead of http://example.com.
-Devise.omniauth_providers.each do |provider|
+Devise.omniauth_providers.map(&:downcase).each do |provider|
   next if provider == 'ldapmain'
   get "/users/auth/-/import/#{provider}/callback", to: "import/#{provider}#callback", as: "users_import_#{provider}_callback"