Incorrect unknown-license-reference detection and misleading license clarity score in recent scan of pyo3-0.20.1.tar.gz

A recent scan of pyo3-0.20.1.tar.gz from https://github.com/PyO3/pyo3/archive/refs/tags/v0.20.1.tar.gz produced generally good results but with a few misleading elements that result in a -20 score for Conflicting license categories.

One problem is the detection of `unknown-license-reference` which apparently is due to this sentence that appears in both the README and CHANGELOG files:

`Dual-license PyO3 under either the Apache 2.0 OR the MIT license. This makes the project GPLv2 compatible. https://github.com/PyO3/pyo3/pull/3108`

The following is more of a question than an issue: ScanCode also detected a `generic-cla` and that's fine but I want to make sure that a CLA Category does not result in a Conflicting license category state when the overall project license is Permissive. If the `generic-cla` is not causing the Conflicting license category state, then that is ok, but if it does that we have a problem, since there should not be any conflict in such a case.

Scan results attached.

[pyo3-0.20.1.tar.gz_scan.zip](https://github.com/nexB/scancode-toolkit/files/13824883/pyo3-0.20.1.tar.gz_scan.zip)