730455a backend: check for the worker liveness less-frequently

Authored and Committed by praiskup 2 years ago
    backend: check for the worker liveness less-frequently
    
    We tend to have up to 200 concurrently running workers nowadays in
    Fedora Copr, and doing liveness check (sending kill) is not for free.
    Let's decrease the frequency of the check from one minute to three
    minutes (most of the builds take more than that).
    
    Merges: #2159