Increase max_average_abs_diff for SharpYuv16Bit

Increase max_average_abs_diff for SharpYuv16Bit from 111.7 to 111.8 for
an upcoming change to libsharpyuv, which trades off conversion quality
for conversion speed.

tests/gtest/avifrgbtoyuvtest.cc

diff --git a/tests/gtest/avifrgbtoyuvtest.cc b/tests/gtest/avifrgbtoyuvtest.cc
index 1ab22dd..54dc993 100644
--- a/tests/gtest/avifrgbtoyuvtest.cc
+++ b/tests/gtest/avifrgbtoyuvtest.cc
@@ -807,7 +807,7 @@
         Values(AVIF_CHROMA_DOWNSAMPLING_SHARP_YUV),
         /*add_noise=*/Values(true),
         /*rgb_step=*/Values(4567),  // High or it would be too slow.
-        /*max_average_abs_diff=*/Values(111.7),  // Sharp YUV introduces some
+        /*max_average_abs_diff=*/Values(111.8),  // Sharp YUV introduces some
                                                  // color shift.
         /*min_psnr=*/Values(49.)  // SharpYuv distortion is acceptable.
         ));