Add RSpec 4 compatibility (#17652)

* Remove outdated option

04078317ba

* Use the non-globally exposed RSpec syntax

https://github.com/rspec/rspec-core/pull/2803

* Use the non-globally exposed RSpec syntax, cont

https://github.com/rspec/rspec-core/pull/2803

* Comply to strict predicate matchers

See:
 - https://github.com/rspec/rspec-expectations/pull/1195
 - https://github.com/rspec/rspec-expectations/pull/1196
 - https://github.com/rspec/rspec-expectations/pull/1277

spec/models/user_api_key_spec.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-describe UserApiKey do
+RSpec.describe UserApiKey do
   describe "#allow?" do
     def request_env(method, path, **path_parameters)
       ActionDispatch::TestRequest.create.tap do |request|