Use GPU special images in two GPU image filter tests

We were always testing the CPU backend.

Bug: skia:9582
Change-Id: I25ff1dc151c1be8a31ab09008393430a1fa85221
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/251457
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed