Remove nullable modifier from author name as it is now never null

Cherry picks f389ef4 as it was lost when merging the branch into 2.x

Author: emmadesilva

packages/framework/src/Framework/Features/Blogging/Models/PostAuthor.php

@@ -34,7 +34,7 @@ class PostAuthor implements Stringable, SerializableContract
     /**
      * The display name of the author.
      */
-    public readonly ?string $name;
+    public readonly string $name;
 
     /**
      * The author's website URL.