Fix typo in #[coroutine] gating error

Author: camelid

compiler/rustc_feature/src/builtin_attrs.rs

@@ -572,7 +572,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // `#[coroutine]` attribute to be applied to closures to make them coroutines instead
     gated!(
         coroutine, Normal, template!(Word), ErrorFollowing,
-        EncodeCrossCrate::No, coroutines, experimental!(coroutines)
+        EncodeCrossCrate::No, coroutines, experimental!(coroutine)
     ),
 
     // RFC 3543

tests/ui/coroutine/gen_block.e2024.stderr

@@ -1,4 +1,4 @@
-error[E0658]: the `#[coroutines]` attribute is an experimental feature
+error[E0658]: the `#[coroutine]` attribute is an experimental feature
   --> $DIR/gen_block.rs:20:13
    |
 LL |     let _ = #[coroutine] || yield true;
@@ -8,7 +8,7 @@ LL |     let _ = #[coroutine] || yield true;
    = help: add `#![feature(coroutines)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: the `#[coroutines]` attribute is an experimental feature
+error[E0658]: the `#[coroutine]` attribute is an experimental feature
   --> $DIR/gen_block.rs:24:13
    |
 LL |     let _ = #[coroutine] || {};

tests/ui/coroutine/gen_block.none.stderr

@@ -44,7 +44,7 @@ LL |     let _ = #[coroutine] || yield true;
    = help: add `#![feature(coroutines)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: the `#[coroutines]` attribute is an experimental feature
+error[E0658]: the `#[coroutine]` attribute is an experimental feature
   --> $DIR/gen_block.rs:20:13
    |
 LL |     let _ = #[coroutine] || yield true;
@@ -54,7 +54,7 @@ LL |     let _ = #[coroutine] || yield true;
    = help: add `#![feature(coroutines)]` to the crate attributes to enable
    = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
 
-error[E0658]: the `#[coroutines]` attribute is an experimental feature
+error[E0658]: the `#[coroutine]` attribute is an experimental feature
   --> $DIR/gen_block.rs:24:13
    |
 LL |     let _ = #[coroutine] || {};

tests/ui/coroutine/gen_block.rs

@@ -18,9 +18,9 @@ fn main() {
     //~^^ ERROR `yield` can only be used in
 
     let _ = #[coroutine] || yield true; //[none]~ ERROR yield syntax is experimental
-    //~^ ERROR `#[coroutines]` attribute is an experimental feature
+    //~^ ERROR `#[coroutine]` attribute is an experimental feature
     //~^^ ERROR yield syntax is experimental
 
     let _ = #[coroutine] || {};
-    //~^ ERROR `#[coroutines]` attribute is an experimental feature
+    //~^ ERROR `#[coroutine]` attribute is an experimental feature
 }