Client forgets login credentials every time it's closed

## Actual behaviour
I go through the connection wizard and enter the server address, username and login, then autofill the rest. That works just fine. I can see and read all the articles visible via the web interface.

However when I close the app and restart it, or the phone reboots etc, the connection details have vanished and I have to re-enter them. The app defaults to starting with a request to go through the connection wizard again.

## Expected behaviour
I'd expect the connection settings to be saved and reloaded correctly every time.

# Steps to reproduce the issue
1. Set up connection.
2. Use connection.
3. Close app.
4. Restart app.
5. No connection saved.

# Environment details
- **wallabag app version**: 2.5.1
- **wallabag app installation source** (e.g. Gplay, F-Droid, manual): F-Droid
- **Android OS version**: 11
- **Android ROM** (e.g. stock, LineageOS, SlimRom,…): stock Android One
- **Android hardware**: Nokia 7.2
- **wallabag server version**: don't know
- **Do you have Two-Factor-Authentication enabled?**: no

# Your experience with wallabag Android app
Other than this issue, it's lovely :)