Using (?i) inside a regex is deprecated. It is still possible to use it
at the start of the regex. I consider it clearer to have the flags as
parameters instead of inside the regex string. So I set the
re.IGNORECASE parameter flag instead.

Also added a test for the function where the regex is used.

Refactored `app.py` to have the getting of data from GitLab using version
4 of the API in its own function. This will help to support GraphQL in
parallel later.