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.

Author: richardlau

test/parallel/parallel.status

@@ -58,6 +58,8 @@ test-runner-watch-mode: PASS,FLAKY
 # https://github.com/nodejs/node/issues/42741
 test-http-server-headers-timeout-keepalive: PASS,FLAKY
 test-http-server-request-timeout-keepalive: PASS,FLAKY
+# https://github.com/nodejs/node/issues/54534
+test-runner-run-watch: PASS, FLAKY
 
 [$arch==arm || $arch==arm64]
 # https://github.com/nodejs/node/pull/31178