Check netloc in urlparse result if path is empty

[a-weiss-programmer]

• Please check if the PR fulfills these requirements

• [x] Tests for the changes have been added

• [ ] Docs have been added / updated

• [x] All CI checks are green

• What kind of change does this PR introduce?

  This fixes a bug where certain versions of urllib will put the results of a parsed file (e.g. file://testing/custom_filters.py::is_invalid_secret) into the netloc property of urlparse instead of the path property.

• What is the current behavior?

  https://github.com/Yelp/detect-secrets/issues/715

• What is the new behavior (if this is a feature change)? The custom filter parser will now check netloc if path is not populated

• Does this PR introduce a breaking change?

  Users should have to make no changes, as it prefers path over netloc

• Other information:

[lorenzodb1]

@a-weiss-programmer thank you for your contribution! Could you advice me on which version have one or the other behaviour?