If for some reason the print sequence is set to one-at-a-time be default in the printer definition
and the number of extruders of the printer is set to >=2, then the print_sequence won't show up in
neither the quality changes nor the user changes, yet it will still have "one-at-a-time" as a
value. In a such case, it will still need to be set to "all-at-once" in the user changes.
This is a theoretical case, as it is very unlikely for a printer to have "one-at-a-time" set by
default in its definition (.def.json) file and still be able to support more than one extruders.
But it is a world full of possibilities out there, so you never know...
CURA-7827