Explicitly depend on poetry-plugin-export

[johnthagen]

See

• https://python-poetry.org/blog/announcing-poetry-1.2.0/#migration-of-the-poetry-export-command

To reflect this, and to accelerate development of the main Poetry project, it has been migrated into a separate repo and is distributed separately as poetry-plugin-export.

To ease the transition, the plugin is installed by default for the 1.2 release. Future releases of Poetry will deprecate this automatic install, and require the user to explicitly install the plugin.

Since nox-poetry depends on poetry-plugin-export, it should document that users must install it or install it as a dependency (if that is supported for poetry plugins? A user might have to opt into this).

[johnthagen]

Note that this will become a more pressing issue because as of Poetry 1.7.0:

Print a future warning that poetry-plugin-export will not be installed by default anymore

• https://github.com/python-poetry/poetry/pull/8562

And perhaps soon:

• https://github.com/python-poetry/poetry/pull/5980

[johnthagen]

A potential Poetry feature that would really help solve this for nox-poetry users is:

• https://github.com/python-poetry/poetry/issues/5729
• https://github.com/python-poetry/poetry/pull/5740