qa/suites/nvmeof: ignore "have only 1 nvmeof gateway"

qa/suites/nvmeof: ignore "have only 1 nvmeof gateway"

Add "have only 1 nvmeof gateway" to ignorelist.
NVMEOF_SINGLE_GATEWAY is already part of ignorelist
but tests sometimes fail on "have only 1 nvmeof gateway".

Thrasher or scalability tests can trigger this but there
are enough asserts to ensure all expected gateways are
up, we can safely ignore this healthcheck warning.

Fixes: https://tracker.ceph.com/issues/75913
Signed-off-by: Vallari Agrawal <vallari.agrawal@ibm.com>