Update PNG script for 1.6.47

Author: blowekamp

Modules/ThirdParty/PNG/UpdateFromUpstream.sh

@@ -8,7 +8,7 @@ readonly name="png"
 readonly ownership="LIBPNG Upstream <png-mng-implement@lists.sourceforge.net>"
 readonly subtree="Modules/ThirdParty/PNG/src/itk$name"
 readonly repo="git://git.code.sf.net/p/libpng/code"
-readonly tag='v1.6.44' # Sept 12, 2024
+readonly tag='v1.6.47'
 readonly paths="
 png*.c
 png*.h