doc: fix comma of the list in worker_threads.md

PR-URL: #26838
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Masashi Hirano <shisama07@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>

Author: nodejh

doc/api/worker_threads.md

@@ -244,7 +244,7 @@ Notable differences inside a Worker environment are:
 - The [`process.stdin`][], [`process.stdout`][] and [`process.stderr`][]
   may be redirected by the parent thread.
 - The [`require('worker_threads').isMainThread`][] property is set to `false`.
-- The [`require('worker_threads').parentPort`][] message port is available,
+- The [`require('worker_threads').parentPort`][] message port is available.
 - [`process.exit()`][] does not stop the whole program, just the single thread,
   and [`process.abort()`][] is not available.
 - [`process.chdir()`][] and `process` methods that set group or user ids