update whatsnew for 2.4.2

revert dependabot sphinx change as it is too recent for RTD

(cherry picked from commit 7e38fc4)

2.4.0 versioning

fix missing rc version tags

2.3.0 version

update github action

add manual trigger

2.2.0 versioning

skip async DoH tests if no httpx

(cherry picked from commit ec5bee7)

remove obsolete download URL; add 3.9 classifier