NetBSD/vax vm for github testing

Jan & John's recent patch to fix perl-5.40 to build on VAX prompted a
comment from perl upstream

"We probably overlooked this due to lack of smoke-testing reports from
non-IEEE fp VAX systems.  Can you suggest how we might get such reports
going forward?"

There is an existing package to run Github CI on NetBSD architectures
supported by qemu - https://github.com/vmactions/netbsd-vm but that doesn't
help VAX.

There is also https://github.com/AaronJackson/2.11BSD-Action which uses
simh to test actions in a 2.11BSD PDP11

If someone were able to combine them we could provide people with a
recommended way to add NetBSD/VAX to their CI pipeline (albeit on github
which is mildly evil, but...)

Much kudos and a starting contribution towards a suitable amount of
caffeine ($100) for anyone up for the challenge :)

David