📝 Make sure the phrase "constant-time compare" actually appears in the docs (GH-93396) (GH-93399)

This is purely for SEO as this is the actual generic name for this kind of method and it currently does not appear in a Google search for "python constant time compare". Not creating an issue or setting this up for backports as its trivial (I think) and not a functional change.
(cherry picked from commit 8241a6971e6051ba10040af6b50f9236faa0c892)

Co-authored-by: Noah Kantrowitz <noah@coderanger.net>