test: mark test_cannot_run_js as flaky
This test has been failing occasionally since it was introduced ~5 days ago. It was the number one failing JS test in the most recent reliability report. Mark it as flaky.
Fixes: https://github.com/nodejs/node/issues/48180 Refs: https://github.com/nodejs/node/pull/47986 Refs: https://github.com/nodejs/reliability/issues/576