Theme reverting back to dark on relaunching despite changing it to light

### Steps to reproduce

1. Launch the electron desktop app, you see the theme being dark
2. Go to `All Settings` -> `Appearance` -> `Theme` and set the theme to light
3. Close the app and build it again
video:

https://user-images.githubusercontent.com/82967080/164610383-5115b6cf-e601-4412-a4e7-a960106db73c.mp4

### Outcome

#### What did you expect?
We expect the theme to be changed to light

#### What happened instead?
The theme goes back to being dark

### Operating system

Ubuntu 18.04.6 LTS

### Application version

_No response_

### How did you install the app?

_No response_

### Homeserver

_No response_

### Will you send logs?

No

Reproduce the issue in the Electron desktop app by following All Settings → Appearance → Theme and selecting light, then close and relaunch or rebuild the app. Trace where the selected theme is persisted and restored; done means the light theme remains active after relaunch.

Written by the indexing model from the issue text.