Build(deps): Bump nox from 2020.12.31 to 2021.6.6 (#386)

* Build(deps): Bump nox from 2020.12.31 to 2021.6.6

Bumps [nox](https://github.com/theacodes/nox) from 2020.12.31 to 2021.6.6.
- [Release notes](https://github.com/theacodes/nox/releases)
- [Changelog](https://github.com/theacodes/nox/blob/main/CHANGELOG.md)
- [Commits](wntrblm/nox@2020.12.31...2021.6.6)

---
updated-dependencies:
- dependency-name: nox
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

* Fix test failure due to `posargs` implementation change in Nox

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Claudio Jolowicz <mail@claudiojolowicz.com>

tests/unit/test_sessions.py

@@ -21,7 +21,7 @@ def iter_sessions() -> IterSessions:
     nox.registry._REGISTRY.clear()
 
     def _iter_sessions() -> Iterator[str]:
-        options = nox._options.options.namespace()
+        options = nox._options.options.namespace(posargs=[])
         manifest = nox.manifest.Manifest(nox.registry.get(), options)
         for session in manifest:
             yield session.name