Update some Skia test expectations due to pre-multiplied alpha changes

Due to changing how pre-multiplied alpha is handled in
https://pdfium-review.googlesource.com/122893, some test cases now
render ever so slightly differently with Skia. Some of this is just
rounding differences.

Bug: 42271020
Change-Id: I977b8e733813bd7e41c8e3c74bdd55d0d616e0c3
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium_tests/+/122970
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Tom Sepez <tsepez@google.com>
17 files changed