Merge pull request #21389 from Gaurav2728/gaurav-unused_require_file

no more require minitest mock here

actionview/test/template/url_helper_test.rb

 require 'abstract_unit'
-require 'minitest/mock'
 
 class UrlHelperTest < ActiveSupport::TestCase
 

activerecord/test/cases/attribute_test.rb

 require 'cases/helper'
-require 'minitest/mock'
 
 module ActiveRecord
   class AttributeTest < ActiveRecord::TestCase

activerecord/test/cases/migration/change_table_test.rb

 require "cases/migration/helper"
-require "minitest/mock"
 
 module ActiveRecord
   class Migration

activerecord/test/cases/migration/pending_migrations_test.rb

 require 'cases/helper'
-require "minitest/mock"
 
 module ActiveRecord
   class Migration