8.7.4: Add support for Poetry 1.2.0+'s dependency groups

[tiegz]

Poetry 1.2.0 added support for dependency groups in https://github.com/python-poetry/poetry/pull/4260 , e.g.:

[tool.poetry.group.test.dependencies]
pytest = "^6.0.0"
pytest-mock = "*"

docs: https://github.com/python-poetry/poetry/blob/1.7.1/docs/managing-dependencies.md#dependency-groups