Skip Startup Scripts in Unit Tests

Gunicorn is replaced with nginx-unit ...

We now serve Netbox with an nginx-unit instance instead of Gunicorn.
This allows us to get rid of the extra Nginx container because Unit is
also serving the static files. The static files are now collected at container
buildtime instead of every startup.

Update images in docker-compose

Fixed test failures because of missing cache ...

When running tests with ´test.sh´ some errors where logged because now
redis-cache instance was running.

Improve test.sh ...

Don't move the original initializers directory, but rather use the one
with the modified initializers in it.

Building the Docker image with Github Actions