selftests/vsock: skip vng setsid workaround on >= 1.41

virtme-ng 1.41 ships the upstream fix for the SIGTTOU hang
(https://github.com/arighi/virtme-ng/pull/453), so the setsid wrapper in
vng_dry_run() is no longer needed there. Gate the workaround on the vng
version: setsid is used for vng < 1.41, and vng is invoked directly on
>= 1.41.

Signed-off-by: Bobby Eshleman <bobbyeshleman@meta.com>
Link: https://patch.msgid.link/20260612-vsock-test-update-v1-2-7d7eeed3ac8f@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>