fix typo

index.bs

@@ -8145,7 +8145,7 @@ Note: Instead of returning an async iterable from an IDL operation, the operatio
     1.  If |nextResult| is an abrupt completion, return [=a promise rejected with=]
         |nextResult|.\[[Value]].
     1.  Let |nextPromise| be [=a promise resolved with=] |nextResult|.\[[Value]].
-    1.  Return the result of [=reacting=] to |nextPromise| with with the following fulfillment
+    1.  Return the result of [=reacting=] to |nextPromise| with the following fulfillment
         steps, given |iterResult|:
         1.  If <a abstract-op>Type</a>(|iterResult|) is not Object, [=JavaScript/throw=] a
             <l spec=ecmascript>{{TypeError}}</l>.