doc: change worker.takeHeapSnapshot to getHeapSnapshot

Adapt doc to match implementation which exports getHeapSnapshot().

PR-URL: https://github.com/nodejs/node/pull/32061
Refs: https://github.com/nodejs/node/pull/31569
Refs: https://github.com/nodejs/node/blob/987a67339518d0380177a2e589f2bbd274230d0e/lib/internal/worker.js#L323


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>