Errors reported in `rustc_lint::levels::LintLevelsBuilder::push` occurs multiple times

[crlf0710]

It seems errors (validation failures) reported from rustc_lint::levels::LintLevelsBuilder::push will occur multiple times. Examples are E0453 (not covered by tests) and E0763 (being added in #73300 , unit test reflecting this problem). I'm not sure what's the best way forward.

[Enselic]

E0453 is actually covered by tests, it's just that its description contains an outdated error message. If you search for "incompatible with previous forbid" you will find the tests.

(I update the description of E0453 in #119388)