Update libpng from 1.6.56 to 1.6.57 (emscripten-forge#5340)

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: 1.6.56
+  version: 1.6.57
 
 package:
   name: ${{ name }}
   version: ${{ version }}
 
 source:
   url: https://downloads.sourceforge.net/project/${{ name }}/libpng16/${{ version }}/${{ name }}-${{ version }}.tar.gz
-  sha256: 8f91e941a07fb1069ebb3855278f82a849e6af14ca05821e14ec3d5348697ea5
+  sha256: 01fdab044cdc575c74a9ef62a4042fbe24fea8bedfe8aa5c89f4467b781bbb60
 
 build:
   number: 0