SDL_image: upgrade vendored libpng to 1.6.54

From b5dec3720df7563d41a45e378b5583b4f96a9e9e Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Tue, 13 Jan 2026 05:10:02 +0300
Subject: [PATCH] upgrade vendored libpng to 1.6.54

---
 .gitmodules     | 2 +-
 external/libpng | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/.gitmodules b/.gitmodules
index f525bddf..507f1cc5 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -5,7 +5,7 @@
 [submodule "external/libpng"]
 	path = external/libpng
 	url = https://github.com/libsdl-org/libpng.git
-	branch = v1.6.53-SDL
+	branch = v1.6.54-SDL
 [submodule "external/libwebp"]
 	path = external/libwebp
 	url = https://github.com/libsdl-org/libwebp.git
diff --git a/external/libpng b/external/libpng
index bed74863..7e498344 160000
--- a/external/libpng
+++ b/external/libpng
@@ -1 +1 @@
-Subproject commit bed748633a146aa6cfea2a959f97e33e5d1451ca
+Subproject commit 7e4983443ad6a62e735e3eb7970eb3a683309dec