Update tests

Author: estebank

library/core/src/default.rs

@@ -106,7 +106,6 @@ use crate::ascii::Char as AsciiChar;
 #[const_trait]
 #[rustc_const_unstable(feature = "const_default", issue = "none")]
 #[rustc_trivial_field_reads]
-#[rustc_const_unstable(feature = "const_default", issue = "none")]
 pub trait Default: Sized {
     /// Returns the "default value" for a type.
     ///

tests/ui/lint/dead-code/unused-struct-derive-default.rs

@@ -9,7 +9,7 @@ struct Used;
 #[derive(Default)]
 enum E {
     #[default]
-    A, //~ ERROR variants `A` and `B` is never constructed
+    A, //~ ERROR variants `A` and `B` are never constructed
     //~^ NOTE `E` has a derived impl for the trait `Default`, but this is intentionally ignored during dead code analysis
     B,
 }