Attempt to send mail template that doesn't exist should be error

This either indicates that the email that should exist doesn't,
or a typo in a fixed template code string. Both of them sound
like an error.

src/Hermes/SendEmailHandler.php

@@ -44,7 +44,7 @@ public function handle(MessageInterface $message): bool
 
         $mailTemplate = $this->apiClient->getTemplate($payload['mail_template_code']);
         if (!$mailTemplate) {
-            Debugger::log("Could not load mail template: record with code [{$payload['mail_template_code']}] doesn't exist");
+            Debugger::log("Could not load mail template: record with code [{$payload['mail_template_code']}] doesn't exist", ILogger::ERROR);
             return false;
         }