FIX: Handle SMTPServerBusy for group smtp email (#13632)

Use the `sidekiq_retry_in` code from Jobs::UserEmail in group SMTP. Also we don't need to keep `seconds_to_delay` -- sidekiq uses the default delay calculation if you return 0 or nil from the block. See 3330df0ee3/lib/sidekiq/job_retry.rb (L216-L234) for sidekiq default retry delay logic.

I experimented with extracting this into a concern or a module, but `sidekiq_retry_in` is quite magic and it would not allow me to abstract away into a module that calls some method specificall in the child job class.

I would love to write tests for this, but it does not seem possible (not sure if its because of our test
setup) to write tests that test sidekiq's retry capability, and I am not sure if we should be anyway. Initial addition
to UserEmail did not test this functionality 
d224966a0e

app/jobs/regular/group_smtp_email.rb

@@ -8,6 +8,19 @@ module Jobs
 
     sidekiq_options queue: 'critical'
 
+    sidekiq_retry_in do |count, exception|
+      # retry in an hour when SMTP server is busy
+      # or use default sidekiq retry formula. returning
+      # nil/0 will trigger the default sidekiq
+      # retry formula
+      #
+      # See https://github.com/mperham/sidekiq/blob/3330df0ee37cfd3e0cd3ef01e3e66b584b99d488/lib/sidekiq/job_retry.rb#L216-L234
+      case exception.wrapped
+      when Net::SMTPServerBusy
+        return 1.hour + (rand(30) * (count + 1))
+      end
+    end
+
     def execute(args)
       return if quit_email_early?
 

app/jobs/regular/notify_mailing_list_subscribers.rb

@@ -12,11 +12,13 @@ module Jobs
     sidekiq_options retry: RETRY_TIMES.size
 
     sidekiq_retry_in do |count, exception|
+      # returning nil/0 will trigger the default sidekiq
+      # retry formula
+      #
+      # See https://github.com/mperham/sidekiq/blob/3330df0ee37cfd3e0cd3ef01e3e66b584b99d488/lib/sidekiq/job_retry.rb#L216-L234
       case exception.wrapped
       when SocketError
-        RETRY_TIMES[count]
-      else
-        ::Jobs::UserEmail.seconds_to_delay(count)
+        return RETRY_TIMES[count]
       end
     end
 

app/jobs/regular/user_email.rb

@@ -8,6 +8,19 @@ module Jobs
 
     sidekiq_options queue: 'low'
 
+    sidekiq_retry_in do |count, exception|
+      # retry in an hour when SMTP server is busy
+      # or use default sidekiq retry formula. returning
+      # nil/0 will trigger the default sidekiq
+      # retry formula
+      #
+      # See https://github.com/mperham/sidekiq/blob/3330df0ee37cfd3e0cd3ef01e3e66b584b99d488/lib/sidekiq/job_retry.rb#L216-L234
+      case exception.wrapped
+      when Net::SMTPServerBusy
+        return 1.hour + (rand(30) * (count + 1))
+      end
+    end
+
     # Can be overridden by subclass, for example critical email
     # should always consider being sent
     def quit_email_early?
@@ -206,22 +219,6 @@ module Jobs
       [message, nil]
     end
 
-    sidekiq_retry_in do |count, exception|
-      # retry in an hour when SMTP server is busy
-      # or use default sidekiq retry formula
-      case exception.wrapped
-      when Net::SMTPServerBusy
-        1.hour + (rand(30) * (count + 1))
-      else
-        ::Jobs::UserEmail.seconds_to_delay(count)
-      end
-    end
-
-    # extracted from sidekiq
-    def self.seconds_to_delay(count)
-      (count**4) + 15 + (rand(30) * (count + 1))
-    end
-
     private
 
     def skip_message(reason)