Roll Skia from 2ba6971bd0d1 to 70988bed1b3b (2 revisions) (#191476)

https://skia.googlesource.com/skia.git/+log/2ba6971bd0d1..70988bed1b3b

2026-08-21 skia-autoroll@skia-public.iam.gserviceaccount.com Manual roll
Dawn from 430122149cc8 to 4bd029589224 (8 revisions)
2026-08-21 robertphillips@google.com Remove
BazelTest-external_client-use_graphite_native_vulkan-default-linux_x64
job

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/skia-flutter-autoroll
Please CC
awolff@google.com,kjlubick@google.com,robertphillips@google.com on the
revert to ensure that a human
is aware of the problem.

To file a bug in Skia: https://bugs.chromium.org/p/skia/issues/entry
To file a bug in Flutter:
https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md