After many tries I just don't think it's worth it to make the tests work
since the repl UX in `pdbpp` is so unreliable in the latest release and
honestly we're trying to go 3.10+ ASAP.
Further,
- entirely drop the pattern matching inside the `do_ctlc()` for now.
- add a `subactor_error` parametrization that catches a case that
previously caused a hang (when you use 'next' immediately after the
first crash/debug lock (the fix was pushed just before this commit).