Importing to checkbox field updates incorrectly

Reproduced this regression on https://wpmaster.demo.civicrm.org/ with 5.55.alpha1 also reported on 5.51.1, 5.53.0:

• Create checkbox custom field with option values of 1,2,3
• Import to this field
• Observe that values in db are now 0,1,2

Pattern:

"1,2,3" becomes => "0,1,2"
"2,3,4" becomes => "1,2,3"

Same behavior exists using labels e.g. Red,Green,Blue.

Importing a singular option value e.g. "2" works as expected.

Ref: https://chat.civicrm.org/civicrm/pl/x1imgh3affbmfb4o9b6ei6fx4h