Update avifinfo_test_12x34_gainmap_tmap.avif

Use instructions at
https://github.com/AOMediaCodec/libavif/blob/16f6a7dda71a27a80fd699e1991f26278d5f0a4f/tests/gtest/avifgainmaptest.cc#L115-L117
to generate the file.

avifdec from libavif failed to decode the 'tmap' derived image item
metadata (introduced in libavif PR #1501).
libavifinfo does not parse the 'tmap' derived image item metadata but
uses libavif at head as a baseline in the avifinfo_tool test.

Change-Id: Idd82c7492f30e3880318b4f6cde48feed708111a
diff --git a/tests/avifinfo_test_12x34_gainmap_tmap.avif b/tests/avifinfo_test_12x34_gainmap_tmap.avif
index 3d26c72..1de29b5 100644
--- a/tests/avifinfo_test_12x34_gainmap_tmap.avif
+++ b/tests/avifinfo_test_12x34_gainmap_tmap.avif
Binary files differ