graphics/py-cartopy: Update to 0.20.1

• Update to 0.20.1 and build against graphics/proj v8
• Add dependency graphics/py-pyproj for coordinate transformations, which added support for building with Proj 8.

Changes:

• https://github.com/SciTools/cartopy/compare/v0.19.0.post1...v0.20.1

PR: 259682, 258313
Reported by: rhurlin
Approved by: maintainer (timeout)