Update libpng to 1.6.46 (#6318)

packages/l/libpng/xmake.lua

@@ -6,6 +6,7 @@ package("libpng")
     add_urls("https://github.com/glennrp/libpng/archive/refs/tags/$(version).tar.gz")
     add_urls("https://github.com/glennrp/libpng.git")
 
+    add_versions("v1.6.46", "767b01936f9620d4ab4cdf6ec348f6526f861f825648b610b1d604167dc738d2")
     add_versions("v1.6.44", "0ef5b633d0c65f780c4fced27ff832998e71478c13b45dfb6e94f23a82f64f7c")
     add_versions("v1.6.43", "fecc95b46cf05e8e3fc8a414750e0ba5aad00d89e9fdf175e94ff041caf1a03a")
     add_versions("v1.6.42", "fe89de292e223829859d21990d9c4d6b7e30e295a268f6a53a022611aa98bd67")