Check directly against meta field name as we only have one

This just makes it all clearer. If/when we add more meta fields, that's something we can revisit then.

packages/publications/src/Models/PublicationType.php

@@ -25,7 +25,6 @@
 use function is_null;
 use function json_decode;
 use function json_encode;
-use function str_starts_with;
 
 /**
  * @see \Hyde\Publications\Testing\Feature\PublicationTypeTest
@@ -183,7 +182,7 @@ public function getFieldDefinition(string $fieldName): PublicationFieldDefinitio
 
     public function getCanonicalFieldDefinition(): PublicationFieldDefinition
     {
-        if (str_starts_with($this->canonicalField, '__')) { // Todo check directly against __createdAt
+        if ($this->canonicalField === '__createdAt') {
             return new PublicationFieldDefinition('string', $this->canonicalField);
         }