editflags: `--vm-type` is not guaranteed to work as an edit flag.

[unsuman]

--vm-type is not guaranteed to work as an edit flag.

e.g., this will probably not work

limactl create --vm-type qemu
limactl edit --vm-type vz

Probably we need a warning when --vm-type is specified as an edit flag for an existing instance, but it can be worked out later.

Originally posted by @AkihiroSuda in #3901 (comment)