Enable Rubocop RSpec/MultipleDescribes (#23672)

.rubocop_todo.yml

@@ -1309,11 +1309,6 @@ RSpec/MissingExampleGroupArgument:
     - 'spec/services/notify_service_spec.rb'
     - 'spec/services/process_mentions_service_spec.rb'
 
-# Offense count: 1
-RSpec/MultipleDescribes:
-  Exclude:
-    - 'spec/routing/well_known_routes_spec.rb'
-
 # Offense count: 599
 RSpec/MultipleExpectations:
   Max: 19

spec/routing/well_known_routes_spec.rb

@@ -1,5 +1,6 @@
 require 'rails_helper'
 
+describe 'Well Known routes' do
   describe 'the host-meta route' do
     it 'routes to correct place with xml format' do
       expect(get('/.well-known/host-meta'))
@@ -13,3 +14,4 @@ describe 'the webfinger route' do
         .to route_to('well_known/webfinger#show')
     end
   end
+end