Disable a few more mtltestprecompile images to avoid flaking.

Change-Id: Icf60ae8fe7042ead63e70947f4a12f50d65bf43a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/439337
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
2 files changed