Update Skia expectations in fx/new/shading_2

CL [1] changed the some Skia layers from type `kOpaque_SkAlphaType` to
`kPremul_SkAlphaType` which affected the edges of images. This CL
updates the affected corpus tests in fx/new/shading_2.

[1] https://pdfium-review.googlesource.com/100930

Bug: pdfium:1855
Change-Id: Ib7aae675e20930f2545ea46949699177e5310ee7
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium_tests/+/102391
Reviewed-by: K. Moon <kmoon@chromium.org>
diff --git a/fx/new/shading_2/shading_2_17_expected_skia.pdf.0.png b/fx/new/shading_2/shading_2_17_expected_skia.pdf.0.png
index 6f8c88d..44d42ea 100644
--- a/fx/new/shading_2/shading_2_17_expected_skia.pdf.0.png
+++ b/fx/new/shading_2/shading_2_17_expected_skia.pdf.0.png
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diff --git a/fx/new/shading_2/shading_2_4_expected_skia.pdf.0.png b/fx/new/shading_2/shading_2_4_expected_skia.pdf.0.png
index 0ecd331..e31bd64 100644
--- a/fx/new/shading_2/shading_2_4_expected_skia.pdf.0.png
+++ b/fx/new/shading_2/shading_2_4_expected_skia.pdf.0.png
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diff --git a/fx/new/shading_2/shading_2_8_expected_skia.pdf.0.png b/fx/new/shading_2/shading_2_8_expected_skia.pdf.0.png
index e798045..9988c4c 100644
--- a/fx/new/shading_2/shading_2_8_expected_skia.pdf.0.png
+++ b/fx/new/shading_2/shading_2_8_expected_skia.pdf.0.png
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diff --git a/fx/new/shading_2/shading_2_9_expected_skia.pdf.0.png b/fx/new/shading_2/shading_2_9_expected_skia.pdf.0.png
index 3135eda..2d46729 100644
--- a/fx/new/shading_2/shading_2_9_expected_skia.pdf.0.png
+++ b/fx/new/shading_2/shading_2_9_expected_skia.pdf.0.png
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diff --git a/fx/new/shading_2/shading_expected_skia.pdf.0.png b/fx/new/shading_2/shading_expected_skia.pdf.0.png
index f08701b..614d17c 100644
--- a/fx/new/shading_2/shading_expected_skia.pdf.0.png
+++ b/fx/new/shading_2/shading_expected_skia.pdf.0.png
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