Add back error type since we aren't changing the parent yet

Author: rebeccahum

WordPress-VIP-Go/ruleset.xml

@@ -96,6 +96,7 @@
 		<severity>6</severity>
 	</rule>
 	<rule ref="WordPressVIPMinimum.Variables.RestrictedVariables.cache_constraints___COOKIE">
+		<type>error</type>
 		<severity>6</severity>
 	</rule>
 	<rule ref="WordPressVIPMinimum.Variables.RestrictedVariables.cache_constraints___SERVER__HTTP_USER_AGENT__">