FIX: Don't notify editor when category or tag change (#17833)

When a user was editing a topic they were also receiving a notification
if they were watching any of the new category or tags.

app/services/post_alerter.rb

@@ -203,8 +203,8 @@ class PostAlerter
 
     warn_if_not_sidekiq
 
-    # Don't notify the OP
+    # Don't notify the OP and last editor
-    user_ids -= [post.user_id]
+    user_ids -= [post.user_id, post.last_editor_id]
     users = User.where(id: user_ids).includes(:do_not_disturb_timings)
 
     DiscourseEvent.trigger(:before_create_notifications_for_users, users, post)

spec/jobs/notify_category_change_spec.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+RSpec.describe ::Jobs::NotifyCategoryChange do
+  fab!(:user) { Fabricate(:user) }
+  fab!(:regular_user) { Fabricate(:trust_level_4) }
+  fab!(:post) { Fabricate(:post, user: regular_user) }
+  fab!(:category) { Fabricate(:category, name: 'test') }
+
+  it "doesn't create notification for the editor who watches new tag" do
+    CategoryUser.set_notification_level_for_category(user, CategoryUser.notification_levels[:watching_first_post], category.id)
+    post.topic.update!(category: category)
+    post.update!(last_editor_id: user.id)
+
+    expect { described_class.new.execute(post_id: post.id, notified_user_ids: []) }.not_to change { Notification.count }
+  end
+end

spec/jobs/notify_tag_change_spec.rb

@@ -40,6 +40,14 @@ RSpec.describe ::Jobs::NotifyTagChange do
     expect { described_class.new.execute(post_id: post.id, notified_user_ids: [regular_user.id]) }.not_to change { Notification.count }
   end
 
+  it "doesn't create notification for the editor who watches new tag" do
+    TagUser.change(user.id, tag.id, TagUser.notification_levels[:watching_first_post])
+    TopicTag.create!(topic: post.topic, tag: tag)
+    post.update!(last_editor_id: user.id)
+
+    expect { described_class.new.execute(post_id: post.id, notified_user_ids: []) }.not_to change { Notification.count }
+  end
+
   it 'doesnt create notification for user watching category' do
     CategoryUser.create!(
       user_id: user.id,