Support `validate_check_constraint` on `Migration/ChangeColumnNull`

[lucasmazza]

I'm adding the gem to our app and testing it against existing migrations, and I noticed that Migration/ChangeColumnNull throws false positives against migrations using validate_check_constraint instead of validate_constraint, like in the following example:

class ReplaceNotNullConstraintOnUsersName < ActiveRecord::Migration[7.0]
  def change
    validate_check_constraint :users, name: :users_name_is_not_null
    change_column_null :users, :name, false
    remove_check_constraint :users, name: :users_name_is_not_null
  end
end

[jbigler]

validate_constraint is used within an alter table block, validate_check_constraint is the standalone command.