devel/py-pytest-cov: Upgrade from 2.9.0 to 4.1.0
This is required so py-pytest-cov is functional with newer versions of
py-pytest-xdist [1].
While here, appease portlint by shifting where variables (CONFLICTS,
etc) are defined.
PR: 269360
Reviewed by: yuri
Approved by: dbaio (maintainer timeout; 5 months)
Co-Authored By: Yuri Victorovich <yuri@freebsd.org>
Differential Revision: https://reviews.freebsd.org/D39035