Various BIND 9.11 (EoL) CI fixes
This merge request ensures the BIND 9.11 (EoL) CI works decently enough to be usable for developing security fixes.
This MR started as isc-private/bind9!646 but has more CI changes - mostly to remove CI jobs, which we can't have because their tooling is changing too rapidly for the EoL branch to keep up with (pylint, clang-format, rolling distributions, ...).
Contrary to isc-private/bind9!646, I dropped BIND 9 code changes that silenced unused variables warning errors and unused assignments, which let some build jobs and the scan-build CI job pass. Instead, I disabled warning errors in the ./configure step and removed the scan-build job entirely. I want to ensure that the BIND 9 code is not changed anywhere, but in security fixes that are delivered as patches; otherwise, it might cause further patches not to be applied cleanly.
Closes #4556 (closed)