Add rubocop-rspec_rails to Rubcop config

Because: It is defined in the Gemfile but not loaded into config

.rubocop.yml

@@ -2,6 +2,7 @@ require:
   - rubocop-performance
   - rubocop-rails
   - rubocop-rspec
+  - rubocop-rspec_rails
   - rubocop-capybara
   - rubocop-factory_bot