Fix wording of misapplied must_not_suspend error

compiler/rustc_passes/messages.ftl

@@ -478,8 +478,8 @@ passes_multiple_start_functions =
     .previous = previous `#[start]` function here
 
 passes_must_not_suspend =
-    `must_not_suspend` attribute should be applied to a struct, enum, or trait
-    .label = is not a struct, enum, or trait
+    `must_not_suspend` attribute should be applied to a struct, enum, union, or trait
+    .label = is not a struct, enum, union, or trait
 
 passes_must_use_async =
     `must_use` attribute on `async` functions applies to the anonymous `Future` returned by the function, not the value within

compiler/rustc_passes/src/check_attr.rs

@@ -1363,7 +1363,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
         }
     }
 
-    /// Checks if `#[must_not_suspend]` is applied to a function.
+    /// Checks if `#[must_not_suspend]` is applied to a struct, enum, union, or trait.
     fn check_must_not_suspend(&self, attr: &Attribute, span: Span, target: Target) {
         match target {
             Target::Struct | Target::Enum | Target::Union | Target::Trait => {}

tests/ui/lint/must_not_suspend/other_items.stderr

@@ -1,10 +1,10 @@
-error: `must_not_suspend` attribute should be applied to a struct, enum, or trait
+error: `must_not_suspend` attribute should be applied to a struct, enum, union, or trait
   --> $DIR/other_items.rs:5:1
    |
 LL | #[must_not_suspend]
    | ^^^^^^^^^^^^^^^^^^^
 LL | mod inner {}
-   | ------------ is not a struct, enum, or trait
+   | ------------ is not a struct, enum, union, or trait
 
 error: aborting due to 1 previous error
 

tests/ui/lint/must_not_suspend/return.stderr

@@ -1,12 +1,12 @@
-error: `must_not_suspend` attribute should be applied to a struct, enum, or trait
+error: `must_not_suspend` attribute should be applied to a struct, enum, union, or trait
   --> $DIR/return.rs:5:1
    |
 LL |   #[must_not_suspend]
    |   ^^^^^^^^^^^^^^^^^^^
 LL | / fn foo() -> i32 {
 LL | |     0
 LL | | }
-   | |_- is not a struct, enum, or trait
+   | |_- is not a struct, enum, union, or trait
 
 error: aborting due to 1 previous error