Fix copy-paste mistake in PQcancelCreate

When an OOM occurred, this function was incorrectly setting a status of
CONNECTION_BAD on the passed in PGconn instead of on the newly created
PGcancelConn.

Mistake introduced with 61461a300c.  Backpatch to 17.

Author: Jelte Fennema-Nio <postgres@jeltef.nl>
Reported-by: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/20240630190040.26.nmisch@google.com

src/interfaces/libpq/fe-cancel.c

@@ -155,7 +155,7 @@ PQcancelCreate(PGconn *conn)
 	return (PGcancelConn *) cancelConn;
 
 oom_error:
-	conn->status = CONNECTION_BAD;
+	cancelConn->status = CONNECTION_BAD;
 	libpq_append_conn_error(cancelConn, "out of memory");
 	return (PGcancelConn *) cancelConn;
 }