doc: fix boldface punctuation for full sentences

If an entire sentence is in boldface, then generally the terminating
punctuation should as well.

PR-URL: https://github.com/nodejs/node/pull/39278


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>