CI: Windows: Fix Docker tag argument inversion

docker tag takes its arguments as source and dest, not dest and source.
Went unnoticed as the host already had a tag for my image when I was
testing.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4346>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4346>

.gitlab-ci/windows/mesa_container.ps1

@@ -27,7 +27,7 @@ if ($?) {
 docker pull "$registry_central_image"
 if ($?) {
   Write-Host "Copying central image $registry_central_image to user image $registry_user_image"
-  docker tag "$registry_user_image" "$registry_central_image"
+  docker tag "$registry_central_image" "$registry_user_image"
   docker push "$registry_user_image"
   $pushstatus = $?
   docker logout "$registry_uri"