Update SBOM external reference type for source code URLs

[tngraf]

As of today we use

{
          "comment": "source archive (download location)",
          "type": "distribution",
          "url": "https://github.com/python-attrs/attrs/archive/tags/26.1.0.zip"
}

which is from CycloneDX 1.4.

For CycloneDX 1.6 and later and for Siemens Standard BOM this should be changed to

{
          "type": "source-distribution",
          "url": "https://github.com/python-attrs/attrs/archive/tags/26.1.0.zip"
}

[gernot-h]

I agree. For the "source archive (local copy)" links, we continue using the distribution type, right?

[tngraf]

I agree. For the "source archive (local copy)" links, we continue using the distribution type, right?

Right