[Bug]: cookiesX.db is not stored in custom conf dir

### ⚠️ Before submitting, please verify the following: ⚠️

- [x] This is a **bug**, not a question or a configuration issue.
- [x] This issue is **not** already reported on Github (I've searched it).
- [x] Nextcloud Server and Desktop Client are **up to date**. See [Server Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) and [Desktop Releases](https://nextcloud.com/install/#install-clients) for supported versions.
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/)

### Bug description

I'm running a "portable" desktop client for testing.

- The client is started like `./Nextcloud-3.15.0-x86_64.AppImage --logdebug --confdir . --logdir .`
- `nextcloud.sync.configfile: Using custom config dir "/home/daniel/Code/nextcloud-desktop"`
- After using the login flow, a file with the cookies is stored in the default location `/home/daniel/.config/Nextcloud/cookies0.db`.

### Steps to reproduce

1. Run the desktop client like above
2. Authenticate
3. See the cookies file is in the wrong location

### Expected behavior

The custom config dir is taken into account

### Which files are affected by this bug

Irrelevant

### Operating system

Linux

### Which version of the operating system you are running.

Irrelevant

### Package

Official Linux AppImage

### Nextcloud Server version

master

### Nextcloud Desktop Client version

3.15.0

### Is this bug present after an update or on a fresh install?

Fresh desktop client install

### Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

### Are you using an external user-backend?

- [x] Default internal user-backend
- [ ] LDAP/ Active Directory
- [ ] SSO - SAML
- [ ] Other

### Nextcloud Server logs

```shell

```

### Additional info

Related to: https://github.com/nextcloud/desktop/issues/5208