devel/py-apispec: Update to 4.2.0
Changelog: https://github.com/marshmallow-code/apispec/blob/dev/CHANGELOG.rst#420-2021-02-06
PR: 253341
Submitted by: Goran Mekic <meka@tilda.center> (maintainer)
Approved by: arrowd, tcberner (mentors, implicit)