Fix sequence membership command in PG19 release notes

The PG19 release-note entry about synchronizing sequence membership [1]
attributes that operation to REFRESH SEQUENCES. It should refer to
REFRESH PUBLICATION.

REFRESH PUBLICATION adds and removes sequence entries in
pg_subscription_rel. REFRESH SEQUENCES instead resets existing sequence
entries to INIT for value resynchronization, without changing which
sequences are subscribed.

This matches the ALTER SUBSCRIPTION reference [2] and the documentation
clarification committed as 19fbb47ef685 [3]. That commit did not update
release-19.sgml.

The attached one-line patch changes the command name in that sentence.
It is based on REL_19_STABLE at a66ab9a9d382 and passes git apply --check.

Regards,
Ruohang Feng
Vonng(at)PGSTY

[1] https://www.postgresql.org/docs/19/release-19.html#RELEASE-19-LOGICAL
[2] https://www.postgresql.org/docs/19/sql-altersubscription.html#SQL-ALTERSUBSCRIPTION-PARAMS-REFRESH-SEQUENCES
[3] https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=19fbb47ef6854b1e3a7311ed2f4e765426e7a611