Replace OpenStruct dependency with Struct

rspec#2754 (comment)

spec/rspec/rails/example/view_example_group_spec.rb

@@ -1,4 +1,3 @@
-require 'ostruct'
 require 'support/group_failure_formatter'
 
 module RSpec::Rails
@@ -188,7 +187,7 @@ def _default_file_to_render; end # Stub method
         Class.new do
           include ViewExampleGroup::ExampleMethods
           def controller
-            @controller ||= ::OpenStruct.new(params: nil)
+            @controller ||= Struct.new(:params).new(nil)
           end
         end.new
       end