src: allow running tasks without `Environment`

There is no real reason to assume that V8 tasks would have
to run in a Node.js `Context`.

PR-URL: https://github.com/nodejs/node/pull/26376


Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>