Tests require pytest < 6 and are impossible fix for now.

* Remove Python 2 support.

enable tests, catch the next FS#51030 style issue early
fix build with attr 2.4.48
python 3.7 rebuild (and related fixes to cython, -Werror)

FTR, commands used to change arch=() and then verify the changes:

$ sed -Ei "/^arch=/{s/ *?['\"]?i686['\"]? *?//;s/ *$//}" */*/PKGBUILD*

$ grep -r i686 * | grep arch= | grep -v repos

$ svn diff | grep -A 1 ^-[^-] | grep -v -- -- | cut -c2- |
  while IFS=$'\n' read -r l1; IFS=$'\n' read -r l2; do
    echo "$l1 -> $l2"
  done | sort -u