Use native nox for tests (not @cs01 fork of nox)

[itsayellow]

• I have added an entry to docs/changelog.md

Summary of changes

Due presumably to updates in virtualenv, and possibly nox, we can now use regular nox for our tests and don't need to use the special fork of nox.

Closes #508

This seems to work fine. However, in the future if we ever notice something that requires venv to be used in nox tests, we can add venv_backend="venv" as an argument to @nox.session() before def tests() in noxfile.py.

Test plan

Tested by running

# command(s) to exercise these changes

[cs01]

Amazing! Thank you. I'm so glad I can delete my branch now.