Update OS images (Fedora 33, OpenBSD 6.8, FreeBSD 12.2)

Update OS images, all are either already out or out in a few weeks.

OpenBSD 6.8: https://gitlab.isc.org/isc-projects/images/-/merge_requests/81
Fedora 33: https://gitlab.isc.org/isc-projects/images/-/merge_requests/82
FreeBSD 12.2: https://gitlab.isc.org/isc-projects/images/-/merge_requests/83
Also there's Ubuntu 20.10 (Groovy Gorilla) a non-LTS release which we don't intend to add to our OS images, but should probably build and test on as a one-off sanity test.

Edited Oct 26, 2020 by Michal Nowak

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