NuGet automatically includes .props file from the build directory in the
target using the package, but only if the .props file has the correct
name: it must be $(id).props
Rename python.props correspondingly in all the nuspec variants. Also
keep python.props as it were for backward compatibility.
(cherry picked from commit 7c11a9acca)
Co-authored-by: Václav Slavík <vaclav@slavik.io>