Disable SkSLIntrinsicPackUnorm2x16 test.
Disable SkSLIntrinsicPackUnorm2x16 test.

This test fails on my work laptop (Radeon 5300M) so simply disabling it
on the tree isn't sufficient in this case. We don't seem to have a test
opt-out mechanism that automatically applies to local runs of dm.

Change-Id: I83582f0cdc3c9e6a61e6dc8e07851b9705143423
Bug: skia:12434
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/447057
Reviewed-by: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Auto-Submit: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>

google/skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia