fix foreign key constraint for variants.instance_question_id
fix foreign key constraint for variants.instance_question_id

kevinwang/PrairieLearn,kevinwang/PrairieLearn,tbretl/PrairieLearn,lotrfan/PrairieLearn,PrairieLearn/PrairieLearnHack,parasgithub/PrairieLearn,lotrfan/PrairieLearn,lotrfan/PrairieLearn,rbessick5/PrairieLearn,PrairieLearn/PrairieLearnHack,kevinwang/PrairieLearn,mwest1066/PrairieLearn,rbessick5/PrairieLearn,tbretl/PrairieLearn,parasgithub/PrairieLearn,PrairieLearn/PrairieLearnHack,kevinwang/PrairieLearn,jakebailey/PrairieLearn,parasgithub/PrairieLearn,rbessick5/PrairieLearn,lotrfan/PrairieLearn,jakebailey/PrairieLearn,kevinwang/PrairieLearn,kevinwang/PrairieLearn,parasgithub/PrairieLearn,PrairieLearn/PrairieLearnHack,lotrfan/PrairieLearn,tbretl/PrairieLearn,jakebailey/PrairieLearn,PrairieLearn/PrairieLearnHack,mwest1066/PrairieLearn,PrairieLearn/PrairieLearnHack,lotrfan/PrairieLearn,PrairieLearn/PrairieLearnHack,kevinwang/PrairieLearn,mwest1066/PrairieLearn,rbessick5/PrairieLearn,mwest1066/PrairieLearn,tbretl/PrairieLearn,rbessick5/PrairieLearn,mwest1066/PrairieLearn,PrairieLearn/PrairieLearnHack,lotrfan/PrairieLearn,tbretl/PrairieLearn,parasgithub/PrairieLearn,jakebailey/PrairieLearn