Have strategy for environment variable handling only once
And provide also a test checking if the environment variables
are present in the forked process.
The strategy applied for setting the environment variables is now
different from what it was before. Before the environment was
fully replaced by the new environment variables. Now we append
our environment variables to the list of environment variables available
by default for the forked process.
Co-authored-by: Florian Geckeler <43751896+fgeckeler@users.noreply.github.com>
