Snapshot main functions are only loaded for main threads in single
executable applications. Update the check to avoid asserting it
in worker threads - this allows worker threads to be spawned in
snapshot main functions bundled into a single executable
application.
PR-URL: https://github.com/nodejs/node/pull/56120
Fixes: https://github.com/nodejs/node/issues/56077
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Joyee Cheung