I don't know; what's the threat model here?

If the script is deliberately malicious as originally published, then the publisher will provide a valid checksum; so it doesn't help.

If the script source is subverted by an attacker, then it only helps if the attacker doesn't also have the means to change the published checksum too.

If an attacker can modify the site which publishes the URL for the script and the checksum, they can modify both at the same time.