Can't publish room in public directory

### Description

Hi!

When I try to publish a room in my host's room directory I get a message saying that there was an error publishing this room. My user has admin rights, and I'm using the Element Web Client.

This happens on the latest version of Synapse (v1.126.0). If I downgrade to the previous version (v1.125.0 or v1.124.0), then it works.

I'm pasting a message that appears on the docker logs when this happens.

Thanks!

### Steps to reproduce

- set up a new instance, create an admin and log in (I tested only on Element Web)
- create a room
- open the settings for this room
- click on "Publish this room to the public in localhost's room directory?"
- the error message pops up and the room does not get published on the public directory

### Homeserver

my custom homeserver (localhost)

### Synapse Version

v1.126.0

### Installation Method

Docker (matrixdotorg/synapse)

### Database

PostgreSQL, single server, new setup

### Workers

I don't know

### Platform

Debian 12 desktop, running on docker 28.0.1 and docker compose v2.33.1

### Configuration

_No response_

### Relevant log output

```shell
matrix_synapse | 2025-03-20 16:33:36,685 - synapse.http.server - 130 - INFO - PUT-100 - SynapseError: 403 - Not allowed to publish room
```

### Anything else that would be useful to know?

_No response_