NuGet scans return LicenseRef-scancode-unknown

### Description

I ran scans on two NuGet packages and it returned the declared license as `LicenseRef-scancode-unknown`.

- [python 3.13.7](https://www.nuget.org/packages/python/3.13.7)
- [7-Zip.Sfx 18.5.0](https://www.nuget.org/packages/7-Zip.Sfx/18.5.0)

```json
"declared_license_expression_spdx": "LicenseRef-scancode-unknown",
"license_detections": [
{
"license_expression": "unknown",
"license_expression_spdx": "LicenseRef-scancode-unknown",
"matches": [
{
"license_expression": "unknown",
"license_expression_spdx": "LicenseRef-scancode-unknown",
"from_file": "codebase/python.nuspec",
"start_line": 1,
"end_line": 1,
"matcher": "5-undetected",
"score": 100.0,
"matched_length": 7,
"match_coverage": 100.0,
"rule_relevance": 100,
"rule_identifier": "package-manifest-unknown-cb3c3d5d7f7cf4a3f3a998e7b68e092ccbfe730d",
"rule_url": "https://github.com/nexB/scancode-toolkit/tree/develop/src/licensedcode/data/rules/package-manifest-unknown-cb3c3d5d7f7cf4a3f3a998e7b68e092ccbfe730d",
"matched_text": "license {'@type': 'file', '#text': 'tools\\\\LICENSE.txt'}"
}
],
"identifier": "unknown-1648570e-f21a-a797-fe5a-e7ce1cb6a377"
}
],
```

On both, it shows a rule match to line 1 in the nuspec. The `rule_url` doesn't work: https://github.com/nexB/scancode-toolkit/tree/develop/src/licensedcode/data/rules/package-manifest-unknown-cb3c3d5d7f7cf4a3f3a998e7b68e092ccbfe730d

Here are the json results:
[7-zip.sfx.18.5.0-results.json](https://github.com/user-attachments/files/23638407/7-zip.sfx.18.5.0-results.json)
[python-3.13.7-results.json](https://github.com/user-attachments/files/23638411/python-3.13.7-results.json)

### How To Reproduce

> Tell us how to reproduce the issue.

`docker run --rm ghcr.io/aboutcode-org/scancode.io:latest run scan_single_package https://api.nuget.org/v3-flatcontainer/python/3.13.7/python.3.13.7.nupkg > results.json`

`docker run --rm ghcr.io/aboutcode-org/scancode.io:latest run scan_single_package https://api.nuget.org/v3-flatcontainer/7-zip.sfx/18.5.0/7-zip.sfx.18.5.0.nupkg > results.json`

### System configuration

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

What OS are you running on? Windows 11 25H2
What version of scancode-toolkit was used to generate the scan file? I think 32.4.0, not sure
What installation method was used to install/run scancode? ScanCode.io instructions in Docker Desktop v4.51.0

I followed the instructions on https://scancodeio.readthedocs.io/en/latest/quickstart.html#run-a-remote-package-scan. If this should be in the scancode.io repo or somewhere else, let me know. I will close this and create a new issue in the correct location.