GTest complains that we don't run some tests on GLES backend.

Bug: chromium:1180570
Change-Id: I9427ac25c3b6f06f3c042caa3c0afc7000cf1599
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2710783Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>