Update libpng from 1.6.55 to 1.6.56 [emscripten-3x] (#5201)

Co-authored-by: emscripten-forge-bot <emscripten-forge-bot@users.noreply.github.com>

Author: emscripten-forge-bot

recipes/recipes_emscripten/libpng/recipe.yaml

@@ -1,14 +1,14 @@
 context:
   name: libpng
-  version: 1.6.55
+  version: 1.6.56
 
 package:
   name: ${{ name }}
   version: ${{ version }}
 
 source:
   url: https://downloads.sourceforge.net/project/${{ name }}/libpng16/${{ version }}/${{ name }}-${{ version }}.tar.gz
-  sha256: 4b0abab6d219e95690ebe4db7fc9aa95f4006c83baaa022373c0c8442271283d
+  sha256: 8f91e941a07fb1069ebb3855278f82a849e6af14ca05821e14ec3d5348697ea5
 
 build:
   number: 0