Fix grammar in monitoring.sgml

This is related to progress reporting for ANALYZE and partitioned
tables.

Author: Amit Langote
Reviewed-by: Daniel Gustafsson, Julien Rouhaud
Discussion: https://postgr.es/m/CA+HiwqGx6C=-bFTX=ryMThyvM7CcSC3b1x8_6zh4Uo41Kvu-zw@mail.gmail.com

doc/src/sgml/monitoring.sgml

@@ -3706,7 +3706,7 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
   <note>
    <para>
     Note that when <command>ANALYZE</command> is run on a partitioned table,
-    all of its partitions are also recursively analyzed as also mentioned on
+    all of its partitions are also recursively analyzed as also mentioned in
     <xref linkend="sql-analyze"/>.  In that case, <command>ANALYZE</command>
     progress is reported first for the parent table, whereby its inheritance
     statistics are collected, followed by that for each partition.