set default scope for callbacks

so that first_or_create works as expected

refs CNVS-15126

Change-Id: Idd87063a06f7c042247735fceff3ae420586052e
Reviewed-on: https://gerrit.instructure.com/41152
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>