Make GitHub workflow uniform

[cyrille-artho]

The GitHub workflow in nhandler is currently a bit different from the other ones:

1. It uses ${HOME}/work as the working directory instead of ${HOME}.
2. It may fail, as mkdir does not use -p.
3. The first line that writes site.properties has >> (append) instead of > (create and overwrite), so the script may be using different (existing) settings rather than new ones.

There are a couple of other minor differences. I recommend adapting the planned new workflow from jpf-nas so we have only one type of workflow, in case we have to troubleshoot it.

[cyrille-artho]

Also, run all the tests in the CI build, as we want to avoid regressions that way.