Check checktest.py related errors shown by our network-health scanners

I often see something like

2020-03-17 21:03:56,973 modules.checktest [ERROR] Check thinks <https://metrics.torproject.org/rs.html#details/296B2178FD742AB35AB20C9ADF04D5DFD3D407EB> isn't Tor.  Desc addr is 206.55.74.0 and check addr is 206.55.74.0.

. We should figure out a) what's up with that and b) whether we actually still need that test to be running.

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