spec: fix conversations api spec role override usage

test plan
- run specs

Change-Id: I6459f71d1a7503ffbe69cd1ea567a7a9f2bc3618
Reviewed-on: https://gerrit.instructure.com/43708
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Braden Anderson <braden@instructure.com>
QA-Review: Braden Anderson <braden@instructure.com>
Product-Review: Braden Anderson <braden@instructure.com>