Use the AttributeDefinedStatically rubocop rule

Factory bot has stopped supporting dynamic attributes, and we'll have to
change all factories before upgrading.

In order to apply the rubocop rule, we need to bump rubocop-rspec to its
latest version.

.rubocop_basic.yml

@@ -20,6 +20,9 @@ Capybara/FeatureMethods:
     - scenario
     - xscenario
 
+FactoryBot/AttributeDefinedStatically:
+  Enabled: true
+
 Layout/IndentationConsistency:
   EnforcedStyle: rails