Utilities/Release: Teach "push" script to create destination subdirectory

Extend the script added by commit 9bf97363b0 (Utilities/Release: Replace
upload step with a "push" script, 2019-05-24, v3.15.0-rc1~56^2) to
create the destination subdirectory for the CMake version being pushed.

Utilities/Release/push.bash

@@ -50,6 +50,9 @@ if test -z "$dir"; then
     dir="v${version}"
 fi
 readonly dir
+if ! test -d "${dest}/${dir}"; then
+    mkdir "${dest}/${dir}"
+fi
 
 for f in cmake-${version}*; do
     if ! test -f "${f}"; then