Clarify that Cow::into_owned returns owned data

Author: jongiddy

library/alloc/src/borrow.rs

@@ -292,8 +292,7 @@ impl<B: ?Sized + ToOwned> Cow<'_, B> {
     ///
     /// # Examples
     ///
-    /// Calling `into_owned` on a `Cow::Borrowed` clones the underlying data
-    /// and becomes a `Cow::Owned`:
+    /// Calling `into_owned` on a `Cow::Borrowed` returns a clone of the borrowed data:
     ///
     /// ```
     /// use std::borrow::Cow;
@@ -307,7 +306,8 @@ impl<B: ?Sized + ToOwned> Cow<'_, B> {
     /// );
     /// ```
     ///
-    /// Calling `into_owned` on a `Cow::Owned` is a no-op:
+    /// Calling `into_owned` on a `Cow::Owned` returns the owned data. The data is moved out of the
+    /// `Cow` without being cloned.
     ///
     /// ```
     /// use std::borrow::Cow;