FIX: add CountryCode to driver's info.

[harningle]

This is to fix #493. We forgot to include CountryCode in the below default_keys when fixing #460:

Fast-F1/fastf1/_api.py

Lines 1493 to 1496 in 89033fd

	default_keys = [
	'RacingNumber', 'BroadcastName', 'FullName', 'Tla', 'Line', 'TeamName',
	'TeamColour', 'FirstName', 'LastName', 'Reference', 'HeadshotUrl'
	]

I also updated the corresponding testing. CountryCode is not generally available in old races, which means the rawdata from the API of our previous test case 70th Anniversary Grand Prix FP2 does not provide drivers' country info., so we can't test our code either. test_driver_list() is now tested against 2023 Bahrain Grand Prix FP1, so that we can check if we correctly parse the CountryCode.

The linting fails as this pushes to the maintenance-v3.1 branch, rather than master.

[theOehrly]

Perfect, thank you 👍