Bump nox from 2020.8.22 to 2020.12.31 in /.github/workflows

Bumps [nox](https://github.com/theacodes/nox) from 2020.8.22 to 2020.12.31.
- [Release notes](https://github.com/theacodes/nox/releases)
- [Changelog](https://github.com/theacodes/nox/blob/master/CHANGELOG.md)
- [Commits](wntrblm/nox@2020.8.22...2020.12.31)

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

Author: dependabot[bot]

.github/workflows/constraints.txt

@@ -1,5 +1,5 @@
 pip==20.3.3
-nox==2020.8.22
+nox==2020.12.31
 poetry==1.1.4
 nox-poetry==0.7.1
 virtualenv==20.2.1