testing/kicad: upgrade to 5.1.12
Upgrades kicad
and kicad-library
to 5.1.12. Also reenables kicad-opencascade
which seems to have been unintentionally disabled in d50164ea (!23893 (merged)). If this change was made intentionally, it would probably be good to document somewhere why it was made and remove the opencascade subpackage split function.