devel/py-munch: Update to 2.4.0

• Add a new dependency at build: devel/py-pbr (required for HEAD)

Changelog:
https://github.com/Infinidat/munch/blob/2.4.0/CHANGELOG.md

PR: 241582
Submitted by: Loïc Bartoletti <lbartoletti@tuxfamily.org> (maintainer)
MFH: 2019Q4