Suppress/skip pep621 manager detection of poetry 2.0 projects

[rarkins]

Describe the proposed change(s).

Currently Poetry 2.0 projects are not recognized by the "poetry" manager, but they are recognized (partially) by the "pep621" manager. We should update the code in https://github.com/renovatebot/renovate/blob/main/lib/modules/manager/pep621/extract.ts so that Poetry 2.0 projects are skipped by the pep621 manager.

This could potentially be done either by looking for signs of poetry in the pyproject.toml, or by looking for a poetry.lock. The pyproject.toml would seem to be more reliable if that is possible.

For now we can assume that "if it's as poetry pyproject.toml, it's not also another pep621 type of project at the same time (e.g. uv)". If someone has a use case where they have both poetry and another pep621 at the same time, we can decide later whether to support that.