Add Fedora 33

I run the Fedora 33 image from staging registry on all maintained branches, all passed:

• v9_11: https://gitlab.isc.org/isc-projects/bind9/-/pipelines/55502
• v9_16: https://gitlab.isc.org/isc-projects/bind9/-/pipelines/55490
• main: https://gitlab.isc.org/isc-projects/bind9/-/pipelines/55487