Updated the SimpleITK version to latest available release 2.4.0.

Update the toolkit version and set the SimpleITK_BUILD_DISTRIBUTE flag
to ON so that the correct version is listed, e.g.
"SimpleITK Version: 2.4.0 (ITK 5.4)" and not
"SimpleITK Version: 2.4.0-ga3e11 (ITK 5.4)"
which is printed without turning the flag on.

configure

@@ -7,7 +7,7 @@
 # Requires git and cmake
 #
 export SimpleITKGit=https://github.com/SimpleITK/SimpleITK
-export SITKTAG=v2.3.0
+export SITKTAG=v2.4.0
 
 export PKGBASED=$(pwd)
 echo ${PKGBASED}