Fix moderator account being exposed in account moderation notification (#30082)

app/models/notification.rb

@@ -184,13 +184,13 @@ class Notification < ApplicationRecord
     return unless new_record?
 
     case activity_type
-    when 'Status', 'Follow', 'Favourite', 'FollowRequest', 'Poll', 'Report', 'AccountWarning'
+    when 'Status', 'Follow', 'Favourite', 'FollowRequest', 'Poll', 'Report'
       self.from_account_id = activity&.account_id
     when 'Mention'
       self.from_account_id = activity&.status&.account_id
     when 'Account'
       self.from_account_id = activity&.id
-    when 'AccountRelationshipSeveranceEvent'
+    when 'AccountRelationshipSeveranceEvent', 'AccountWarning'
       # These do not really have an originating account, but this is mandatory
       # in the data model, and the recipient's account will by definition
       # always exist

spec/models/notification_spec.rb

@@ -138,6 +138,17 @@ RSpec.describe Notification do
         expect(notification.account).to eq(account)
       end
     end
+
+    context 'when activity_type is an AccountWarning' do
+      it 'sets the notification from_account to the recipient of the notification' do
+        account = Fabricate(:account)
+        account_warning = Fabricate(:account_warning, target_account: account)
+
+        notification = Fabricate.build(:notification, activity_type: 'AccountWarning', activity: account_warning, account: account)
+
+        expect(notification.from_account).to eq(account)
+      end
+    end
   end
 
   describe '.preload_cache_collection_target_statuses' do