Typo in get_devices type hint

[le91688]

Fix fields parameter type hint in get_devices function

Issue Description:

The fields parameter of the get_devices function in the lariat.py file is currently using the wrong syntax for the type hint. We need to fix the type hint and ensure that mypy does not report any errors for the function.

Current function signature

def get_devices(client: SwaggerClient,
                request_opts: typing.Dict,
                fields=typing.Optional[typing.List[str]]) -> typing.List[Device]:

Correct function signature:

def get_devices(client: SwaggerClient,
                request_opts: typing.Dict,
                fields: typing.Optional[typing.Set[typing.Any]) -> typing.List[Device]:

Mypy is also currently not configured to enforce type hints, so disallow_untyped_defs = True should be added to mypy.ini to catch any future of these issues