Update supported versions and dependencies#509

Merged

zerolab merged 10 commits intowagtail:mainfrom zerolab:chore/wagtail-216-and-deps

Jan 26, 2022

+11,697-237

Commits on Jan 20, 2022

Allow running tests on Wagtail 2.16 (currently via main)
zerolab
committed

Commits on Jan 25, 2022

Commits on Jan 26, 2022

Test against Django 4.0 (and Wagtail main)
zerolab
committed