Run full testing via GH Actions (#1810)

* Run more tests via github actions

* Fix the syntax

* Simplify the Python build

* Install the missing requirements

* Switch to 20.04 to match Travis

* Add 3.9, tidy up a bit

* Add a comment about latest aspell

* Update codespell-private.yml

Co-authored-by: Eric Larson <larson.eric.d@gmail.com>