[bazel] Add --keep_going to IWYU job

Devs who cannot run IWYU locally (yet) should get more detailed
errors from this and require fewer CQ jobs to fix any errors.

Change-Id: Icdbfba3feaeadb6c180fb1d3ea4a754b8d3ce51d
Bug: skia:12541
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/532402
Reviewed-by: John Stiles <johnstiles@google.com>
1 file changed