Autofix Rubocop RSpec/LeadingSubject (#23670)

spec/services/process_mentions_service_spec.rb

@@ -1,10 +1,10 @@
 require 'rails_helper'
 
 RSpec.describe ProcessMentionsService, type: :service do
-  let(:account) { Fabricate(:account, username: 'alice') }
-
   subject { ProcessMentionsService.new }
 
+  let(:account) { Fabricate(:account, username: 'alice') }
+
   context 'when mentions contain blocked accounts' do
     let(:non_blocked_account)          { Fabricate(:account) }
     let(:individually_blocked_account) { Fabricate(:account) }