test/test_device: do not enforce a password

[benma]

According to the type in HardwareWalletClient, password is optional and can be None:

def __init__(self, path: str, password: Optional[str], expert: bool, chain: Chain = Chain.MAIN) -> None:

The test code also expects that it can be None, e.g.:

https://github.com/bitcoin-core/HWI/blob/d774d65255e1e78ea4d97846c2b4d26a23febcfb/test/test_device.py#L140

The BitBox02 client in fact checks that it must be None and raises a BadArgumentError otherwise, as the BitBox02 does not accept any password/passphrase from the host:

https://github.com/bitcoin-core/HWI/blob/d774d65255e1e78ea4d97846c2b4d26a23febcfb/hwilib/devices/bitbox02.py#L266

Other devices like the Jade also don't take a host password/passphrase, and simply ignore the param. We could also do this for the BitBox02 (not raise any error if a password is supplied), but the right solution is to not enforce a password in the tests.

This commit is in preparation of adding a BitBox02 simulator with tests.