chore: ignore HTTP 403 errors (#1481)

Update the CloudWatch error alarm so that requests that
generate an HTTP 403 response do not trigger the alarm.

This is being done because fuzzing attacks will often
generate 403 responses for requests that include at least
one of the error alarm's filter words.

infrastructure/terragrunt/aws/alarms/locals.tf

@@ -17,6 +17,7 @@ locals {
     "action=lostpassword&error",
     "database error",
     "GET /notification-gc-notify/wp-json/wp/v2/pages",
+    "HTTP/1.1\\\" 403",
     "HTTP/1.1\\\" 404",
   ]
   wordpress_database_errors = [