In #10721, the seaborn stubs depend on matplotlib that only included a py.typed marker file in version 3.8.
matplotlib version 3.8 requires python >=3.9 which leads to the mypy tests failing on python 3.8.

Alex Waygood suggests adding a requires-python field to METADATA.toml and teaching stub-uploader to include it in the generated setup.py #10721 (comment).

Please let us know what you think about this idea or if you have another solution.