Clarify #[derive(PartialEq)] on enums

Fixes #97945

Author: eggyal

library/core/src/cmp.rs

@@ -61,8 +61,8 @@ use self::Ordering::*;
 ///
 /// This trait can be used with `#[derive]`. When `derive`d on structs, two
 /// instances are equal if all fields are equal, and not equal if any fields
-/// are not equal. When `derive`d on enums, each variant is equal to itself
-/// and not equal to the other variants.
+/// are not equal. When `derive`d on enums, two instances are equal if they
+/// are the same variant and all fields are equal.
 ///
 /// ## How can I implement `PartialEq`?
 ///