Replace --python with --try-first-with

[hexmode]

If a tool like asdf provides a python that is first in the path, virtualenv does not use it even though it is the one used to invoke poetry. Using --try-first-with (introduced in 20.3.0) allows poetry to point to the prefered python.

See https://virtualenv.pypa.io/en/latest/changelog.html#v20-3-0-2021-01-10 Resolves: #9278