* fix(gw): validate requested CAR version
This adds validation of 'application/vnd.ipld.car;version=n' passed
in the Accept header by HTTP clients to align Gateway behavior with
the spec submitted to IANA.
* test: fix comment in test/sharness/t0118-gateway-car.sh
Co-authored-by: Gus Eggert <gus@gus.dev>
Co-authored-by: Gus Eggert <gus@gus.dev>