[Release test] Disabling empty-runtime-env tests in benchmark_worker_startup.aws #35232

This test uses some hackery to get a "default" (empty) runtime environment on Anyscale. This allows us to measure startup performance for non-Anyscale environments. We validate that the numbers are correct by asserting empty runtime env for these measurements. Since our infra team recently added cgroup to the default runtime env, the assertion now fails.

We can fix this but not a priority right now -- this PR disables the empty-runtime-env tests in this release test, so we still have metrics for the normal path.

Closes #35183