www/py-falcon: update to 3.1.3

Switch to DISTVERSION.
Pet portfmt, portclippy.

Changelogs:
https://github.com/falconry/falcon/releases/tag/3.1.3
https://github.com/falconry/falcon/releases/tag/3.1.1
https://github.com/falconry/falcon/releases/tag/3.1.0

PR: 280252
Approved by: lichray <lichray@gmail.com> (maintainer)