CI Pipeline does not use installed timor version

Summary

Currently, the CI pipeline installs timor-python, but then, the import timor statements in the unittest will work with the local files instead of the pip package installed from them due to the src directory being the working directory.

Steps to reproduce

Run the current CI pipeline. To see the issue, cd into timor-python/src and call import timor, timor.__file__ - you will see, that the local init file will be displayed, not the one located in the pip package.

What is the current bug behavior?

The CI does not test the installed package, which it should do.

Possible fixes

Do not cd into src in the gitlab-ci.yaml. This will require some reworking of the coverage reporting, which failed earlier when we did not do that

/cc @JonathanKuelz