py.typed marker file not included in published wheel

Related to #223

The changes from #224 should have resulted in the py.typed marker file being included in the published wheel (following the [instructions in the setuptools docs](https://setuptools.pypa.io/en/latest/userguide/datafiles.html#package-data) and the [example package](https://github.com/emmatyping/pep-561) included in [PEP561](https://peps.python.org/pep-0561/)

When I build the package locally, the file is included; however, the layout I get in the locally built wheel is slightly different than the published version, so there is definitely some configuration or setuptools/wheel version difference.