Re-revert "pythonPackages.flaky: 3.5.3 -> 3.6.1 (#68411)"
Re-revert "pythonPackages.flaky: 3.5.3 -> 3.6.1 (#68411)"

This reverts commit a95a53aadc3a84ff8c2660f44aa124c58da241cd.
i.e. the change is moved from the master branch to staging.

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs