doc: Adding a partition does not require Access Exclusive lock

This doc update was missed in 898e5e3290.  Backpatch to 12.

Pointed out by Pavel Luzanov
Discussion: https://postgr.es/m/642e9fbc-b832-698b-9a8f-d626afd7014d@postgrespro.ru

doc/src/sgml/ddl.sgml

@@ -4121,8 +4121,8 @@ ALTER INDEX measurement_city_id_logdate_key
       <listitem>
        <para>
         Some operations require a stronger lock when using declarative
-        partitioning than when using table inheritance.  For example, adding
-        or removing a partition to or from a partitioned table requires taking
+        partitioning than when using table inheritance.  For example,
+        removing a partition from a partitioned table requires taking
         an <literal>ACCESS EXCLUSIVE</literal> lock on the parent table,
         whereas a <literal>SHARE UPDATE EXCLUSIVE</literal> lock is enough
         in the case of regular inheritance.