BUG #18649: PG17 release note bug for "AS LOCAL"

The following bug has been logged on the website:

Bug reference:      18649
Logged by:          TAKATSUKA Haruka
Email address:      harukat@sraoss.co.jp
PostgreSQL version: 17.0
Operating system:   any
Description:

The following "AS LOCAL" should be "AT LOCAL".

doc/src/sgml/release-17.sgml:
<!--
Author: Michael Paquier <michael@paquier.xyz>
2023-10-13 [97957fdba] Add support for AT LOCAL
-->

     <listitem>
      <para>
      Allow the session <link linkend="guc-timezone">time zone</link>
      to be specified by <literal>AS LOCAL</literal> (Vik Fearing)
      <ulink url="&commit_baseurl;97957fdba">§</ulink>
      </para>

      <para>
      This is useful when converting adding and removing time zones from
      time stamps values, rather than specifying the literal session
      time zone.
      </para>
     </listitem>