Transfer dependency to --dev in poetry

You can move the corresponding line in the pyproject.toml from the [tool.poetry.dependencies] section to [tool.poetry.dev-dependencies] by hand and run poetry lock --no-update afterwards.

You can also poetry add -D <dep> and poetry remove <dep> in either order. Just be sure to use the same version constraint. Poetry stops/warns you if you use different constraints as they'd conflict.