Update libpng to v1.6.42 (#3217)

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("v1.6.42", "fe89de292e223829859d21990d9c4d6b7e30e295a268f6a53a022611aa98bd67")
     add_versions("v1.6.40", "62d25af25e636454b005c93cae51ddcd5383c40fa14aa3dae8f6576feb5692c2")
     add_versions("v1.6.37", "ca74a0dace179a8422187671aee97dd3892b53e168627145271cad5b5ac81307")
     add_versions("v1.6.36", "5bef5a850a9255365a2dc344671b7e9ef810de491bd479c2506ac3c337e2d84f")