doc PG 17 relnotes: adjust IN wording

Reported-by: David Rowley

Discussion: https://postgr.es/m/CAApHDvqmW0wQRam4paRbHvLQA+w5CJOCno4BCu=NFRLRhYhtRw@mail.gmail.com

Backpatch-through: master

Author: bmomjian

doc/src/sgml/release-17.sgml

@@ -467,7 +467,7 @@ Author: Peter Geoghegan <pg@bowt.ie>
 
 <listitem>
 <para>
-Allow btree indexes to more efficiently find a set of values, such as those supplied by IN subqueries (Peter Geoghegan, Matthias van de Meent)
+Allow btree indexes to more efficiently find a set of values, such as those supplied by IN clauses using constants (Peter Geoghegan, Matthias van de Meent)
 </para>
 </listitem>