Disable rrl check in slow environments

The check for 'would limit' log message is triggered by sending at least three messages within one second. However, in extremely slow conditions (currently when running with clang+TSAN in CI), the individual queries might take too much time to send enough of them within one second.

Since this is a pretty rare condition, let's just silently skip this test in environments where a single query takes more than 500 ms, since there's no way to perform the check under such conditions.

Closes #4082 (closed)