Annex C: Change 3.0 Model URL to new one at spdx.org

[bact]

• https://spdx.github.io/spdx-3-model/model.ttl -> https://spdx.org/rdf/3.0.0/spdx-model.ttl
  • New IRI according to 2024-04-02 Tech call

The https://spdx.github.io/spdx-3-model/model.ttl can probably a model in development (in 3.x.x) and not stable.

We may want to use the public-facing IRI: https://spdx.org/rdf/3.0.0/spdx-model.ttl (which will be redirected to https://spdx.github.io/spdx-spec/v3.0/model/spdx-model.ttl).

Note: As the link is specifically to 3.0.0, we have to update this for 3.0.1 and later

[bact]

@goneall I closed #924 after I messed up with rebase during an attempt to do DCO.

Please review this PR instead. Apology for any inconvenience. Thank you.