pythonPackages.uvloop: 0.12.2 -> 0.13.0 (#67735)

* As mentioned in https://github.com/NixOS/nixpkgs/issues/67492
the build was broken after an update of openssl versions.

* Fixes a flake8 unit-test case that requires a flake8 config
which is not shipped with the distribution.

* Fixes build on darwin.