Regression in debsrc package license detection

### Description

While working on updating the version of ScanCode that's being used by the ClearlyDefined service, I noticed that I believe to be a bug/regression.

Somewhere between `scancode-toolkit` versions 30 and 32, there must have happened a small regression which leads to the license of the `python-tenacity` package not being detected correctly anymore.

Running on the debsrc `python-tenacity` package version 8.2.1-1 with `scancode-toolkit` `30.1.0` yields a license expression result of `apache-2.0` whereas `scancode-toolkit` `32.0.8` returns an empty `declared_license_expression`. Looking at the [package's copyright file](https://metadata.ftp-master.debian.org/changelogs//main/p/python-tenacity/python-tenacity_8.2.1-1_copyright), Apache 2.0 should be the correct and expected result.

Here's the raw data as output by the ClearlyDefined crawler when running `scancode-toolkit` on the package (which also includes the exact versions and command line arguments):

https://github.com/clearlydefined/service/blob/2392fafba5c03c6b1beb4ecd526baea8b62ca04d/test/fixtures/scancode/30.1.0/debsrc-license-expression.json

https://github.com/clearlydefined/service/blob/2392fafba5c03c6b1beb4ecd526baea8b62ca04d/test/fixtures/scancode/32.0.8/debsrc-license-expression.json