Scancode is not correctly scanning some licenses

### Description

We have a project dependency on mapbox-gl which contains this line in their package.json:
`"license": "SEE LICENSE IN LICENSE.txt",`
I'll link the LICENSE.txt file [here](https://github.com/mapbox/mapbox-gl-js/blob/main/LICENSE.txt)
When I run scancode, I get `licenseref-scancode-unknown-license-reference`.

I also get unknown license reference for js-cookie and css-declaration-sorter, which have very normal license definitions, `"license": "MIT",` and `"license": "ISC",` respectively.

Finally, I get `licenseref-scancode-unknown` for an internal package with `"license": "UNLICENSED",` in its package.json.

### How To Reproduce

Install any of the mentioned packages (mapbox-gl, js-cookie, or css-declaration-sorter) and run scancode

`scancode --verbose --license --package --processes=4 --json-pp scan_results.json --include package.json --include *.txt .`

### System configuration

> For bug reports, it really helps us to know:

* What OS are you running on? (Windows/MacOS/Linux)
* Linux
* What version of scancode-toolkit was used to generate the scan file?
* What installation method was used to install/run scancode? (pip/source download/other)
* pip