[21.05] python3Packages.pywemo: disable failing test

[mweinelt]

Motivation for this change

With libxml2 2.9.12 this test started failing, it was reported upstream
at pywemo/pywemo#268.

(cherry picked from commit a0160c0)

Backport #124385

ZHF #122042

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Added a release notes entry if the change is major or breaking
• Fits CONTRIBUTING.md.

[risicle]

Got to say, I don't really understand this new libxml2 2.9.12 behaviour. Seems pretty wrong to me. Edit to answer self: most of this is likely due to https://gitlab.gnome.org/GNOME/libxml2/-/issues/255

[mweinelt]

Might not need to backport this if we fix the libxml2 issue in the first place, so setting this to blocked.

[jonringer]

This builds on staging-next-21.05, where the libxml2 patch was applied

[11:56:41] jon@nixos ~/projects/nixpkgs (staging-next-21.05)
$ nix-build -A python3Packages.pywemo
/nix/store/v3c8dy23556p8d5mx503sk6gwmy2zahk-python3.8-pywemo-0.6.4
[11:56:44] jon@nixos ~/projects/nixpkgs (staging-next-21.05)