Add missing isolation test for test_decoding in meson build
Oversight in
7f13ac8, where catalog_change_snapshot was missing from the
list in meson.build.
Author: Hayato Kuroda
Discussion: https://postgr.es/m/TYAPR01MB58662C932F45A13C6F9BE352F5259@TYAPR01MB5866.jpnprd01.prod.outlook.com