glossary.rst: Fix typo in package definition (GH-98865)

This is a tiny typo fix of package definition in glossary.
According to https://devguide.python.org/documentation/help-documenting/ simple typos don’t require issues of their own, but, instead, a pull request can by submitted directly.

Automerge-Triggered-By: GH:AlexWaygood
(cherry picked from commit fc94d55ff453a3101e4c00a394d4e38ae2fece13)

Co-authored-by: ab <abousselmi@users.noreply.github.com>