~~https://github.com/NixOS/nixpkgs/pull/89514~~
While this is just a version bump (and adding myself as maintainer, as there currently aren’t any maintainers listed for pytest-rerunfailures) it does fix
~~Issues · NixOS/nixpkgs · GitHub
which was caused by
python3Packages.pytest: 5.3.5 -> 5.4.1 · NixOS/nixpkgs@adb485b · GitHub
and currently blocks installation of depending package xonsh on nixos-unstable.