Documentation for gRPC Credential issue on POSIX references fco

I came accross the know issue where on POSIX it is required to specify the root certs.

There is documentation here on how to do this in InfluxDBClient3:
https://docs.influxdata.com/influxdb/clustered/reference/client-libraries/v3/python/#specify-the-root-certificate-path

It references that `fco=flight_client_options(...)` in the example, however this does not actually populate the flight_client_options object.
The syntax should be `flight_client_options=flight_client_options(...)` in order for the object to populated correctly.

Open the linked InfluxDBClient3 Python documentation and find the root certificate example. Check the flight client options assignment shown there, then correct the argument name so the object is populated. Done means the published example uses the corrected syntax and remains consistent with the surrounding instructions.

Written by the indexing model from the issue text.