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">&sect;</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>