Update Skia expectations for image shifts

Updates Skia-specific expectations for single-pixel shifts of image
objects relative to AGG, due to acceptable rounding and anti-aliasing
differences.

Bug: pdfium:1856
Change-Id: Id3da587eef63a460ec9f5ba9a623c20a9be94f57
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium_tests/+/103330
Reviewed-by: Nigi <nigi@chromium.org>