test: use ppc and ppc64 to skip SEA tests on PowerPC

It seems using ppc alone is not enough. Add ppc64 to be safe.

PR-URL: nodejs#50828
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Keyhan Vakil <kvakil@sylph.kvakil.me>

test/sequential/sequential.status

@@ -47,7 +47,7 @@ test-watch-mode-inspect: PASS, FLAKY
 # https://github.com/nodejs/node/issues/41286
 test-performance-eventloopdelay: PASS, FLAKY
 
-[$arch==ppc]
+[$system==ppc || $system==ppc64]
 # https://github.com/nodejs/node/issues/50740
 test-single-executable-application-empty: PASS, FLAKY
 test-single-executable-application-snapshot-and-code-cache: PASS, FLAKY