LGTM.com - false positive - unused import in Python

**Description of the false positive**

The tests for `unused import` are causing false positives.
For example, inn the URL shown below, there's an `import pytextrank` which loads a factory for customized components within `spaCy` pipelines. Usage of this dependency happens during the `add_pipe()` pipeline calls in `spaCy`, as of the 3.x releases.

See for details.
CC: @ines

This kind of false positive will likely also be the case in popular Python libraries that use "plugin" architectures, such as [`rdflib`](https://rdflib.readthedocs.io/).

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

https://lgtm.com/projects/g/DerwenAI/pytextrank/snapshot/722e794d5db71885acef44eaf0c48e2ec3d4b204/files/sample.py?sort=name&dir=ASC&mode=heatmap#x523ba5599d0f7367:1