Cannot collect package metadata for Debian

### Description

I am using scancode to scan container images like Debian. I have recently seen that scancode does not inventory Debian packages.

### How To Reproduce

It's somewhat lengthy but you can get a debian root fs and run scancode against it. I will attach the json I got from it.

### System configuration

* What OS are you running on? Ubuntu 20.04 LTS
* What version of scancode-toolkit was used to generate the scan file? 21.2.25
* What installation method was used to install/run scancode? pip
[scancode.debian.json.txt](https://github.com/nexB/scancode-toolkit/files/6224272/scancode.debian.json.txt)