DEV: Remove remaining hardcoded ids (#18735)

spec/models/topic_spec.rb

@@ -2801,7 +2801,7 @@ RSpec.describe Topic do
   end
 
   describe '#pm_with_non_human_user?' do
-    fab!(:robot) { Fabricate(:user, id: -3) }
+    fab!(:robot) { Fabricate(:bot) }
 
     fab!(:topic) do
       topic = Fabricate(:private_message_topic,

spec/models/user_spec.rb

@@ -1992,7 +1992,7 @@ RSpec.describe User do
 
   describe '.human_users' do
     it 'should only return users with a positive primary key' do
-      Fabricate(:user, id: -1979)
+      Fabricate(:bot)
       user = Fabricate(:user)
 
       expect(User.human_users).to eq([user])