doc: Fix DocBook XML validity

See 3a9d430a.  A new one snuck in.

doc/src/sgml/config.sgml

@@ -4132,10 +4132,11 @@ local0.*    /var/log/postgresql
      </varlistentry>
 
      <varlistentry id="guc-cluster-name" xreflabel="cluster_name">
-      <term><varname>cluster_name</varname> (<type>string</type>)</term>
+      <term><varname>cluster_name</varname> (<type>string</type>)
       <indexterm>
        <primary><varname>cluster_name</> configuration parameter</primary>
       </indexterm>
+      </term>
       <listitem>
        <para>
         Sets the cluster name that appears in the process title for all