Update libpng to v1.6.49 (#7542)

packages/l/libpng/xmake.lua

@@ -6,6 +6,7 @@ package("libpng")
     add_urls("https://github.com/glennrp/libpng/archive/refs/tags/$(version).tar.gz",
              "https://github.com/glennrp/libpng.git")
 
+    add_versions("v1.6.49", "e425762fdfb9bb30a5d2da29c0067570e96b5d41d79c659cf0dad861e9df738e")
     add_versions("v1.6.48", "b17e99026055727e8cba99160c3a9a7f9af788e9f786daeadded5a42243f1dd0")
     add_versions("v1.6.47", "631a4c58ea6c10c81f160c4b21fa8495b715d251698ebc2552077e8450f30454")
     add_versions("v1.6.46", "767b01936f9620d4ab4cdf6ec348f6526f861f825648b610b1d604167dc738d2")