devel/py-ttkbootstrap: Update to 1.20.0

• Fix pyproject.toml (via a post-patch target), because the build framework does not recognise its new format. (see https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license-and-license-files )

ChangeLog: https://github.com/israel-dryer/ttkbootstrap/releases/tag/v1.20.0
Reported by: portscout!