doc: escape elements swallowed as HTML in markdown

Addresses Markdownlint MD033 issues.
Altering changlog should usually be avoided, but they don't render
currently.

PR-URL: https://github.com/nodejs/node/pull/29374


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>