Make GLSLTest_ES31.MixOfAllResources more lenient. Lower precision in Vulkan caused off-by-one issues with this test. BUG=angleproject:4438 Change-Id: I17111a06133ef403be1f0c99321f1dbf8ab6083c Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2078791 Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>