Project environment creation doesn't respect version specifiers in requires-python

[charliermarsh]

Per https://github.com/charliermarsh/autobot/actions/runs/9454139177/job/26041035557?pr=4, it looks like requires-python = ">=3.8" gets parsed as an executable named >=3.8. I think stringifying there probably never works for requires-python? But I'd have to look at the tests to understand whether there's some case it is handling today.