update ui tests

Author: GuillaumeGomez

src/test/ui/gated-bad-feature.stderr

@@ -30,4 +30,5 @@ LL | #![feature = "foo"]
 
 error: aborting due to 5 previous errors
 
-For more information about this error, try `rustc --explain E0557`.
+Some errors have detailed explanations: E0556, E0557.
+For more information about an error, try `rustc --explain E0556`.