bpo-43207: InspectLoader.is_package is not an abstract method (GH-24517)


Making the description of `InspectLoader.is_package` aligned with the current implementation.

Automerge-Triggered-By: GH:jaraco
(cherry picked from commit 8b9310d90281d4bd3643f4e0767b2d0390f0cb05)

Co-authored-by: Junnosuke Kuroda <Isa-rentacs@users.noreply.github.com>