Roll Skia from c74d2bdbd93c to b56003bf2c20 (2 revisions) (flutter#175665)

https://skia.googlesource.com/skia.git/+log/c74d2bdbd93c..b56003bf2c20

2025-09-19 vigneshv@google.com BitmapRegionDecoder: Enable AVIF support
2025-09-19 ccameron@chromium.org SkPngRustDecoder: Add HDR metadata
support

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/skia-flutter-autoroll
Please CC
chinmaygarde@google.com,kjlubick@google.com,michaelludwig@google.com on
the revert to ensure that a human
is aware of the problem.

To file a bug in Skia: https://bugs.chromium.org/p/skia/issues/entry
To file a bug in Flutter:
https://github.com/flutter/flutter/issues/new/choose

To report a problem with the AutoRoller itself, please file a bug:
https://issues.skia.org/issues/new?component=1389291&template=1850622

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/main/autoroll/README.md

Author: engine-flutter-autoroll

DEPS

@@ -14,7 +14,7 @@ vars = {
   'flutter_git': 'https://flutter.googlesource.com',
   'skia_git': 'https://skia.googlesource.com',
   'llvm_git': 'https://llvm.googlesource.com',
-  'skia_revision': 'c74d2bdbd93c809e84df34d4e184b3e5858e5200',
+  'skia_revision': 'b56003bf2c20b7c16344da43e21a2670bab88419',
 
   # WARNING: DO NOT EDIT canvaskit_cipd_instance MANUALLY
   # See `lib/web_ui/README.md` for how to roll CanvasKit to a new version.