Spam check only when Snippet / Issue "title" or "description" are changed

With this MR we're narrowing when the spam check is triggered and properly presenting the errors when trying to update the description with an AJAX call (i.e. task lists).

EE Backport gitlab-ee!1479

See #29483 (closed), #29645 (closed) for more info.

Screenshots (if relevant)

Closes #29483 (closed), #29645 (closed)