This should prevent flakiness in this test.

Bug: angleproject:5245
Change-Id: I841de2cee093ea04b35763314f0a4f5497bcf778
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2497223Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>