Update corpus expectations for MultiplyAlpha()

Updates corpus expectations to account for minor alpha differences after
reimplementing CFX_SkiaDeviceDriver::MultiplyAlpha() with native Skia
operations.

Bug: pdfium:1949
Change-Id: I71ceb266922a80c918b0a7ce9733998bd9b6391d
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium_tests/+/105330
Reviewed-by: Nigi <nigi@chromium.org>
7 files changed