Allow always send forward email

The new key only block notifications emails from Dashboard::Mailer.
Fix specs.

app/mailers/dashboard/mailer.rb

@@ -1,6 +1,6 @@
 class Dashboard::Mailer < ApplicationMailer
   layout "mailer"
-  after_action :check_deliverability
+  after_action :check_deliverability, except: [:forward]
 
   def forward(proposal)
     @proposal = proposal

spec/mailers/dashboard/mailer_spec.rb

@@ -20,12 +20,12 @@ describe Dashboard::Mailer do
       ActionMailer::Base.deliveries.clear
     end
 
-    it "Disables email delivery using setting" do
+    it "Disables notification emails delivery using setting, does not affect the forward email" do
       Setting["feature.dashboard.notification_emails"] = nil
 
       Dashboard::Mailer.forward(proposal).deliver_now
 
-      expect(ActionMailer::Base.deliveries.count).to eq(0)
+      expect(ActionMailer::Base.deliveries.count).to eq(1)
     end
 
     it "sends forward email" do