fix: typeof msg should compare to object (#75221)
### Fixing a bug
The code is located at
https://github.com/vercel/next.js/blob/c33eb2b6505f6717a1a1eac10e193da9d9fa1ece/packages/next/src/server/lib/start-server.ts#L429
`typeof msg` should be compared to `'object'`. Otherwise, it makes no
sense.
