Notification mechanism when scheduled tests fail

[honno]

We now have a cronjob, but no notification mechanism when it fails. It'd be nice if there was a notification mechanism on failures. I'm assuming auto-generating GH issues should be trivial (probably not creating new ones if an open issue already exists), otherwise just sending an email to me, so I'll have to explore this at some point. ^{For now, one can look at https://github.com/data-apis/dataframe-interchange-tests/actions}