Description of the false positive

The warning [1] is only valid for older Python versions, but invalid for Python 3.8, which was released in October 2019.

[1] Keyword argument 'dirs_exist_ok' is not a supported parameter name of function (shutil.)copytree.

URL to the alert on the project page on LGTM.com

https://lgtm.com/projects/g/sosy-lab/cpachecker/snapshot/600369b90877446fdb27ab169736c5c2ad7b7e84/files/scripts/cpa_witness2test.py?sort=name&dir=ASC&mode=heatmap#x4edcecaac134f276:1