25.7.0 stopped working with KWallet6

**Describe the bug**

With 25.7.0, there's no KWallet backend any more in the list of backends:

```
[~]> keyring --list-backends
keyring.backends.fail.Keyring (priority: 0)
keyring.backends.chainer.ChainerBackend (priority: 10)
keyring.backends.SecretService.Keyring (priority: 5)
keyring.backends.libsecret.Keyring (priority: 4.8)
```

With 25.6.0 the list looks like this:

```
[~]> keyring --list-backends
keyring.backends.libsecret.Keyring (priority: 4.8)
keyring.backends.kwallet.DBusKeyringKWallet4 (priority: 4.1)
keyring.backends.fail.Keyring (priority: 0)
keyring.backends.chainer.ChainerBackend (priority: 10)
keyring.backends.SecretService.Keyring (priority: 5)
keyring.backends.kwallet.DBusKeyring (priority: 5.1)
```

This makes applications that use `python-keyring` to fail while reading previously stored secrets when running under KDE.

**To Reproduce**

It's Arch Linux, and I've just installed the newest `python-keyring` package version. As far as I can see the version bump in the `PKGBUILD`, there were no other changes in packaging, so it must be something with the `python-keyring` code itself.

**Expected behavior**

I'd expect apps like `gajim` or `osc` to work with KWallet, but they stopped working after installing this update.

**Environment**

- OS: Arch Linux
- `python-keyring` package version `25.7.0-1`
- KDE, everything latest&greatest

**Additional context**

Please help me diagnose this further.

Thank you.

Start by reproducing `keyring --list-backends` with versions 25.7.0 and 25.6.0 in the reported KDE environment, then inspect the 25.7.0 backend discovery and KWallet-related changes. Done means the KWallet backends are listed again and applications can read previously stored secrets under KDE.

Written by the indexing model from the issue text.