Set important mailer headers with `after_action` callback (#32057)

app/mailers/admin_mailer.rb

@@ -9,6 +9,8 @@ class AdminMailer < ApplicationMailer
   before_action :process_params
   before_action :set_instance
 
+  after_action :set_important_headers!, only: :new_critical_software_updates
+
   default to: -> { @me.user_email }
 
   def new_report(report)
@@ -56,12 +58,6 @@ class AdminMailer < ApplicationMailer
   def new_critical_software_updates
     @software_updates = SoftwareUpdate.where(urgent: true).to_a.sort_by(&:gem_version)
 
-    headers(
-      'Importance' => 'high',
-      'Priority' => 'urgent',
-      'X-Priority' => '1'
-    )
-
     locale_for_account(@me) do
       mail subject: default_i18n_subject(instance: @instance)
     end
@@ -82,4 +78,12 @@ class AdminMailer < ApplicationMailer
   def set_instance
     @instance = Rails.configuration.x.local_domain
   end
+
+  def set_important_headers!
+    headers(
+      'Importance' => 'high',
+      'Priority' => 'urgent',
+      'X-Priority' => '1'
+    )
+  end
 end