test: mark test-runner-run-watch flaky on macOS

`parallel/test-runner-run-watch` has failed 33 out of the last 100
CI runs on macOS. It is already marked flaky on other platforms.

PR-URL: #60115
Refs: #54534
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: richardlau

test/parallel/parallel.status

@@ -79,6 +79,8 @@ test-cluster-dgram-1: SKIP
 [$arch==arm]
 # https://github.com/nodejs/node/issues/63835
 test-fs-utimes-y2K38: SKIP
+# https://github.com/nodejs/node/issues/54534
+test-runner-run-watch: PASS, FLAKY
 
 [$arch==arm || $arch==arm64]
 # https://github.com/nodejs/node/pull/31178