Minor template error -> Wrong subnet linked

https://github.com/acantril/aws-dev-associate/blob/3b19cbe9c00b203d9156a8418019cde27130f204/09-VPCBasics/05_private_internet_access_using_nat_gateways/A4L_NATGateways.yaml#L33

Points to the web B subnet, though is meant to be for the web C subnet (based on naming and lesson context)