Media overwrites validation constraints

I made a patch proposal fix for this issue.

Thanks @miksha. The merge request needs to be created against 11.x (our main development branch); it will be backported to supported versions once committed to 11.x. In some cases the easiest thing to do is close the previous merge request and create a new one against 11.x.

@xjm I created https://git.drupalcode.org/project/drupal/-/merge_requests/8349