Unauthorised users can create topics

[baldrich25]

🐞 Describe the bug
Unauthorised users can send a request to create a topic, the user is provided a 40301, however the topic is still created.

💻 Components impacted
ntfy server

💡 Screenshots and/or logs

🔮 Additional context
Using the builtin metrics server, you can monitor the count of topics on the server at a given time.

When sending unauthorised requests to publish to a topic, the user is provided a 4031 however the metric count still goes up, suggesting the topic is actually create on the server, the user just had no rights to join the topic.