Bump nox from 2020.12.31 to 2021.6.12 in /.github/workflows

Bumps [nox](https://github.com/theacodes/nox) from 2020.12.31 to 2021.6.12.
- [Release notes](https://github.com/theacodes/nox/releases)
- [Changelog](https://github.com/theacodes/nox/blob/main/CHANGELOG.md)
- [Commits](wntrblm/nox@2020.12.31...2021.6.12)

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

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

.github/workflows/constraints.txt

@@ -1,5 +1,5 @@
 pip==21.1.2
-nox==2020.12.31
+nox==2021.6.12
 nox-poetry==0.8.6
 poetry==1.1.6
 virtualenv==20.4.7