Support auto-extending a similar dependency requirement with different `python_version` marker

[CasperWA]

It would be cool if the update_deps task checks the listed supported Python versions for at package and checks all of them for the given packages. If it then finds that some requirements should be split according to that requirement dropping Python support for a given version, it could split the requirement accordingly, effectively adding 1+ "new" requirement lines to the pyproject.toml.