Bump nox from 2019.11.9 to 2020.5.24 in /.github/workflows

Bumps [nox](https://github.com/theacodes/nox) from 2019.11.9 to 2020.5.24.
- [Release notes](https://github.com/theacodes/nox/releases)
- [Changelog](https://github.com/theacodes/nox/blob/master/CHANGELOG.md)
- [Commits](wntrblm/nox@2019.11.9...2020.5.24)

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

Author: dependabot[bot]

.github/workflows/constraints.txt

@@ -1,3 +1,3 @@
 pip==20.1.1
-nox==2019.11.9
+nox==2020.5.24
 poetry==1.0.5