AppVeyor: update to Ubuntu2004 image, for up-to-date SSL certificates for Savannah, for gnulib
AppVeyor: update to Ubuntu2004 image, for up-to-date SSL certificates for Savannah, for gnulib

AbiWord/enchant,AbiWord/enchant,AbiWord/enchant,rrthomas/enchant,AbiWord/enchant,rrthomas/enchant,rrthomas/enchant,rrthomas/enchant