Add Oxford comma to security warning list

Co-authored-by: jkotas <[email protected]>

Author: Copilot

xml/System.Buffers/ArrayPool`1.xml

@@ -311,7 +311,7 @@ The array returned by this method may not be zero-initialized.
 Once a buffer has been returned to the pool, the caller gives up all ownership of the buffer and must not use it. The reference returned from a given call to the <xref:System.Buffers.ArrayPool%601.Rent%2A> method must only be returned using the <xref:System.Buffers.ArrayPool%601.Return%2A> method once. The default <xref:System.Buffers.ArrayPool%601> may hold onto the returned buffer in order to rent it again, or it may release the returned buffer if it's determined that the pool already has enough buffers stored.
 
 > [!IMPORTANT]
-> Returning the same array reference twice or continuing to use the array reference after it has been returned is a high-severity security issue. These actions can lead to [double-free](https://cwe.mitre.org/data/definitions/415.html) and [use-after-free](https://cwe.mitre.org/data/definitions/416.html) vulnerabilities, which might result in data corruption, data leaks and denial of service.
+> Returning the same array reference twice or continuing to use the array reference after it has been returned is a high-severity security issue. These actions can lead to [double-free](https://cwe.mitre.org/data/definitions/415.html) and [use-after-free](https://cwe.mitre.org/data/definitions/416.html) vulnerabilities, which might result in data corruption, data leaks, and denial of service.
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         </remarks>
       </Docs>