python3-pytest: depend on python3-tomli instead of python3-toml

Since version 7.0.0 [1], pytest switched from the toml package to the
tomli package for parsing pyproject.toml configuration files [2].

This change is not immediately noticable during tests, because the
toml/tomli module is only important if a pyproject.toml is actually
present in a project.

[1] https://docs.pytest.org/en/latest/changelog.html#pytest-7-0-0rc1-2021-12-06
[2] https://github.com/pytest-dev/pytest/issues/8789



Signed-off-by: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Steve Sakoman <steve@sakoman.com>