Add stricter e-mail validation for on push notification

E-mail validation is using Devise's regexp pattern
instead of checking for the existence of `@` symbol

Changelog: changed

app/models/integrations/emails_on_push.rb

@@ -13,9 +13,7 @@ module Integrations
     validate :number_of_recipients_within_limit, if: :validate_recipients?
 
     def self.valid_recipients(recipients)
-      recipients.split.select do |recipient|
-        recipient.include?('@')
-      end.uniq(&:downcase)
+      recipients.split.grep(Devise.email_regexp).uniq(&:downcase)
     end
 
     def title

spec/models/integrations/emails_on_push_spec.rb

@@ -78,9 +78,10 @@ RSpec.describe Integrations::EmailsOnPush do
   end
 
   describe '.valid_recipients' do
-    let(:recipients) { '<invalid> foobar Valid@recipient.com Dup@lica.te dup@lica.te Dup@Lica.te' }
+    let(:recipients) { '<invalid> foobar valid@dup@asd Valid@recipient.com Dup@lica.te dup@lica.te Dup@Lica.te' }
 
     it 'removes invalid email addresses and removes duplicates by keeping the original capitalization' do
+      expect(described_class.valid_recipients(recipients)).not_to contain_exactly('valid@dup@asd')
       expect(described_class.valid_recipients(recipients)).to contain_exactly('Valid@recipient.com', 'Dup@lica.te')
     end
   end