Which mirrors to test?

In our (daily) routine mirror checks, we compute the list of mirrors to test by parsing https://download.kiwix.org/mirrors.html

This list is built periodically based on _enabled_ mirrors. So if we manually disable one mirror, it doesn't appear in the list and is thus not tested. That works fine.

When a mirror is down and not manually disabled, mirrorbrain (mirrorprobe) sets its `status_baseurl` to false and thus the mirror is not used in responses but it's still included in that list of mirrors. That makes sense because it's enabled and *expected*.

Made me question if that's the appropriate list of things to test.

Start by reviewing the daily mirror-check routine that parses https://download.kiwix.org/mirrors.html and the mirrorbrain (mirrorprobe) handling of status_baseurl. Determine which mirror set should be tested when enabled mirrors are down or manually disabled; the issue is done when the expected test list is explicitly defined and implemented.

Written by the indexing model from the issue text.