New notifications form resets whenever I try to change something

### Steps to reproduce

1. Join the new notification settings beta
2. Go to notification settings
3. Click the mysterious 'switch now' button (what does it do?)
4. Toggle the 'mentions and keywords' checkbox

### Outcome

#### What did you expect?

I should see my change reflected in the form

#### What happened instead?

The change gets undone a second later, and then the form becomes disabled again and shows the mysterious 'switch now' button once more

[Screencast from 2023-07-10 15-12-18.webm](https://github.com/vector-im/element-web/assets/48614497/1fbde536-2117-48f8-9d07-36f06d201109)

### Operating system

NixOS unstable

### Browser information

Firefox 114.0.1

### URL for webapp

develop.element.io

### Application version

Element version: 311c5fec664d-react-186497a67d09-js-e68a1471c12c Olm version: 3.2.14

### Homeserver

Unable to check the version right now, ping me if relevant

### Will you send logs?

Yes

Start in the notification settings flow of the web app and reproduce the issue using the beta, the “switch now” button, and the mentions and keywords checkbox. Trace why the form becomes disabled and resets; done means the checkbox change remains reflected in the form and the switch button does not reappear unexpectedly.

Written by the indexing model from the issue text.