Editorial: Update note on duplicate [[OwnPropertyKeys]] entries

Co-authored-by: ExE Boss <[email protected]>

Author: shvaikalesh

index.bs

@@ -8259,8 +8259,8 @@ ECMAScript Object values.
             1.  Let |typedValue| be |value| [=converted to an IDL value=] of type |V|.
             1.  [=map/Set=] |result|[|typedKey|] to |typedValue|.
 
-                Note: it's possible that |typedKey| is already in |result|, if |O| is a proxy
-                object.
+                Note: It's possible that |typedKey| is already in |result|,
+                if |K| is {{USVString}} and |key| contains unpaired surrogates.
     1.  Return |result|.
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