GitHub wf update

[sjohansson]

Update to the pipeline definition:

• Use newer versions of actions/gh versions of actions
• Use .net 8 (up from 6)
• Use latest DocFx version (currently 2.76), install through dotnet command
• Should resolve dependencies on deprecated node runners

this should resolve the build warnings spawned from current version.
Needs some testing in this repo to make sure it runs as expected/same as in other repos