fix: Cannot refer to other var in validation

Author: gtoonstra

variables.tf

@@ -780,11 +780,6 @@ variable "datadog_api_key" {
   type        = string
   default     = ""
   sensitive   = true
-
-  validation {
-    condition     = var.monitor_lambda_datadog ? length(var.datadog_api_key) > 0 : true
-    error_message = "Datadog API key must be provided when monitoring Lambda with Datadog"
-  }
 }
 
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