Update AggregateException.xml (#10396)

Author: epsitec

xml/System/AggregateException.xml

@@ -672,8 +672,8 @@
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>Returns the <see cref="T:System.AggregateException" /> that is the root cause of this exception.</summary>
-        <returns>The <see cref="T:System.AggregateException" /> that is the root cause of this exception.</returns>
+        <summary>Returns the <see cref="T:System.Exception"/> that is the root cause of this exception. This exception is either the root exception or the first <see cref="T:System.AggregateException"/> that contains either multiple inner exceptions or no inner exceptions at all.</summary>
+        <returns>The <see cref="T:System.Exception" /> that is the root cause of this exception.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>