Change "Changing a Release tag is only supported via Releases API" helper text

Proposal

Remove the "Changing a Release tag is only supported via Releases API" helper text on the Edit Release page.

Why?

It's not actually possible to change a release's tag, even through the API. Attempting to change a release's tag_name through the API will result in the tag_name parameter being ignored.

Proposal

Change the text to be The tag name can't be changed for an existing release.