spec: fix external tool controler flakey spec failing
spec: fix external tool controler flakey spec failing

This is the investion that we did to understand why this spec is failing:
https://instructure.atlassian.net/browse/INTEROP-6587?focusedCommentId=1120609

closes INTEROP-6587
flag=none

test-plan:
- specs should pass
- running flakey spec local should pass:

docker-compose exec -T -e FORCE_FAILURE=0 web bash \
  -c 'cd /usr/src/app && bundle exec flakey_spec_catcher \
  --repeat=5 \
  --output=/usr/src/app/tmp/fsc.out \
  --test=./spec/controllers/external_tools_controller_spec.rb,\
  ./spec/apis/auth_spec.rb \
  --use-parent'

Change-Id: I5122baa0d2b69577e24e83960aacafb5fd046d04
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/259940
Reviewed-by: Tucker Mcknight <4b51b98c1d84aa97854d216bd061ce5d3eda8a28@instructure.com>
QA-Review: Tucker Mcknight <4b51b98c1d84aa97854d216bd061ce5d3eda8a28@instructure.com>
Product-Review: Wagner Goncalves <1386d52ba3130eb1a5647e5b47f1073537d5ef43@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>

sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms