Add private method for event export filename (#38454)

app/controllers/severed_relationships_controller.rb

@@ -13,13 +13,13 @@ class SeveredRelationshipsController < ApplicationController
 
   def following
     respond_to do |format|
-      format.csv { send_data following_data, filename: "following-#{@event.target_name}-#{@event.created_at.to_date.iso8601}.csv" }
+      format.csv { send_data following_data, filename: }
     end
   end
 
   def followers
     respond_to do |format|
-      format.csv { send_data followers_data, filename: "followers-#{@event.target_name}-#{@event.created_at.to_date.iso8601}.csv" }
+      format.csv { send_data followers_data, filename: }
     end
   end
 
@@ -48,4 +48,8 @@ class SeveredRelationshipsController < ApplicationController
   def acct(account)
     account.local? ? account.local_username_and_domain : account.acct
   end
+
+  def filename
+    "#{action_name}-#{@event.identifier}.csv"
+  end
 end