Use correct type for catalog_xmin

Commit 85c17f6 mistakenly declared a variable storing catalog_xmin as
XLogRecPtr, even though catalog_xmin is a TransactionId.

This caused no functional issue, but the type was clearly incorrect.
Therefore, this commit fixes it to use the correct type TransactionId
instead, and backpatch to v17 where the issue was introduced.

Author: Imran Zaheer <imran.zhir@gmail.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/CA+UBfa=mNeLt-4BFjEP4tqdDsnq+oMqqPr7fd9Wji2_9YXmQdA@mail.gmail.com

src/backend/replication/logical/slotsync.c

@@ -340,7 +340,7 @@ update_local_synced_slot(RemoteSlot *remote_slot, Oid remote_dbid)
 			bool		found_consistent_snapshot;
 			XLogRecPtr	old_confirmed_lsn = slot->data.confirmed_flush;
 			XLogRecPtr	old_restart_lsn = slot->data.restart_lsn;
-			XLogRecPtr	old_catalog_xmin = slot->data.catalog_xmin;
+			TransactionId old_catalog_xmin = slot->data.catalog_xmin;
 
 			LogicalSlotAdvanceAndCheckSnapState(remote_slot->confirmed_lsn,
 												&found_consistent_snapshot);