SDL_image: upgrade vendored libpng to 1.6.47

From e33e204667b3310d280c8b88fe327190b3777036 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Wed, 26 Feb 2025 17:55:10 +0300
Subject: [PATCH] upgrade vendored libpng to 1.6.47

---
 external/libpng | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/external/libpng b/external/libpng
index f98df89f1..d5f3b7303 160000
--- a/external/libpng
+++ b/external/libpng
@@ -1 +1 @@
-Subproject commit f98df89f110248450c1552e69c6346b1c901a453
+Subproject commit d5f3b730390cbbf9f1086a4aa97b7d44e42919ae