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This solves the problem where the used pyenv is actually the one in a
Windows folder, instead of in WSL.

Fixes #9034

This is needed if in between the update of `$PATH` the `$commands` parameter hasn't
been updated, i.e. if there was no `rehash` or `hash -rf` or automatic rehash.
Co-authored-by: Marc Cornellà <marc.cornella@live.com>

* Refactor pyenv plugin to use PATH

Check pyenv-virtualenv can eval before use it.
Signed-off-by: Superbil <superbil@gmail.com>