Enable AllowImplicitReturn:false for Rails/SaveBang rubocop rule

This rule prevents usage of nonbang actions inside block/method.
This commit also adds ActionDispatch::TestRequest into AllowedReceivers,
in order to prevent accidental usage of bang operator.

.rubocop.yml

@@ -471,6 +471,8 @@ Rails/TimeZone:
 # WIP: See https://gitlab.com/gitlab-org/gitlab/-/issues/220040
 Rails/SaveBang:
   Enabled: true
+  AllowImplicitReturn: false
+  AllowedReceivers: ['ActionDispatch::TestRequest']
   Include:
     - 'spec/**/*.rb'
     - 'ee/spec/**/*.rb'