Change wording for sign up regex restrictions

app/models/user.rb

@@ -1825,7 +1825,7 @@ class User < ApplicationRecord
     return if restrictions.blank?
 
     if Gitlab::UntrustedRegexp.new(restrictions).match?(email)
-      errors.add(:email, _('is not allowed for sign-up'))
+      errors.add(:email, _('is not allowed. Try again with a different email address, or contact your GitLab admin.'))
     end
   end
 

locale/gitlab.pot

@@ -24028,7 +24028,7 @@ msgstr ""
 msgid "is not a valid X509 certificate."
 msgstr ""
 
-msgid "is not allowed for sign-up"
+msgid "is not allowed. Try again with a different email address, or contact your GitLab admin."
 msgstr ""
 
 msgid "is not an email you own"

spec/models/user_spec.rb

@@ -529,7 +529,7 @@ describe User, :do_not_mock_admin_mode do
             user = build(:user, email: 'info@gitlab.com')
 
             expect(user).not_to be_valid
-            expect(user.errors.messages[:email].first).to eq(_('is not allowed for sign-up'))
+            expect(user.errors.messages[:email].first).to eq(_('is not allowed. Try again with a different email address, or contact your GitLab admin.'))
           end
 
           it 'does accept a valid email address' do