/available-ips/ response code incorrect for newer Netbox versions

[kyle-burnett]

Since v3.1.1 Netbox returns 409 for exhausted prefixes instead of 204 netbox-community/netbox#7519

So this check no longer works and the tests fail once the prefix is full:

netbox-loadtest/helpers/netbox.py

Lines 54 to 55 in a32eb79

	if result.status_code == 204:
	raise RuntimeError

Not sure if this is maintained or not, so just putting this here incase anyone else tries to use this on newer Netbox versions