doc: Fix description of target_session_attrs=prefer-standby
If no standbys can be found in the set of connection points provided,
the fallback behavior is "any", and not "all" that does not exist.
Author: Greg Nancarrow
Discussion:
@@ -1965,7 +1965,7 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
<listitem>
<para>
first try to find a standby server, but if none of the listed
- hosts is a standby server, try again in <literal>all</literal>
+ hosts is a standby server, try again in <literal>any</literal>
mode
</para>
</listitem>
