fix(google_cloudsql_mysql): Allow null values for connector_enforcement

Same fix as #223 for
MySQL

Author: jbuck

google_cloudsql_mysql/variables.tf

@@ -16,7 +16,7 @@ variable "connector_enforcement" {
   description = "Enables the enforcement of Cloud SQL Auth Proxy or Cloud SQL connectors for all the connections. If enabled, all the direct connections are rejected."
 
   validation {
-    condition     = var.connector_enforcement == null || contains(["NOT_REQUIRED", "REQUIRED"], var.connector_enforcement)
+    condition     = var.connector_enforcement == null ? true : contains(["NOT_REQUIRED", "REQUIRED"], var.connector_enforcement)
     error_message = "Valid values for connector_enforcement: NOT_REQUIRED, REQUIRED"
   }
 }