Merge pull request rails#49123 from skipkayhil/hm-followup-49090

Remove $global mistakenly left in test

Author: guilleiguaran

activerecord/test/cases/migration/compatibility_test.rb

@@ -783,8 +783,6 @@ def migrate(x)
       end
     }.new(nil, 0)
 
-    $global = true
-
     change_migration = Class.new(migration_class) {
       def migrate(x)
         change_column :more_testings, :published_at, :datetime