Update libpng to v1.6.48 (#7247)

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("v1.6.48", "b17e99026055727e8cba99160c3a9a7f9af788e9f786daeadded5a42243f1dd0")
     add_versions("v1.6.47", "631a4c58ea6c10c81f160c4b21fa8495b715d251698ebc2552077e8450f30454")
     add_versions("v1.6.46", "767b01936f9620d4ab4cdf6ec348f6526f861f825648b610b1d604167dc738d2")
     add_versions("v1.6.44", "0ef5b633d0c65f780c4fced27ff832998e71478c13b45dfb6e94f23a82f64f7c")