python LS: add support for os.getenv() completions

[austin3dickey]

Addresses part of #11259. Adds support for os.getenv(" env var completions.

Release Notes

New Features

• N/A

Bug Fixes

• N/A

QA Notes

import os

os.getenv("
os.getenv('
os.getenv(key="
os.getenv(default="  # shouldn't show env vars
os.getenv("", "")  # try either string; second shouldn't show env vars

[github-actions]

E2E Tests 🚀
This PR will run tests tagged with: @:critical

^{readme  valid tags}

[seeM]

Hmm it doesn't seem to be working for me, is this something on my side?

[austin3dickey]

@seeM You'll need to import os first. At first I thought this was a bug, but I looked at the behavior before the refactor and it looks like os.getenv(" never worked without context about what you imported. 🙂