doc: change "it's" to "its" where necessary

PR-URL: https://github.com/nodejs/node/pull/36913


Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Pooja D P <Pooja.D.P@ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>