Bug #10288: Fix newly identified issues to make our test suite more robust and faster
"Fetching OpenPGP keys" scenarios are fragile
bertagaz said on #12290#note-8 that these failures had disappeared in September, so I'm not flagging these scenarios as fragile: instead, while doing #12292 anonym should check this and act accordingly, hence making this a Research ticket on anonym's plate for this month.
Wrt. the best long-term option we've selected on #12211 ("Run a local mock keyserver onion. This doesn't depend on the Internet => potentially 100% robust"), I've read that Schleuder 3 does mock the keyserver in its test suite. Likely that's in Ruby so we could maybe reuse it easily :)