[develop] Use MAJOR.MINOR version JSON-LD context URL in example

[bact]

This PR targets develop branch.
A similar PR for support/3.0 is at #1247

To use "3.0"/"3.1" RDF URLs (version without patch version), as required by spdx/spdx-3-model#1046, we need to verify if new RDF URLs are working.

We may check that with an SBOM example (examples/jsonld/package_sbom.json) and the example validation workflow in this repo.

This issue may not directly affect the texts in the ISO publication but without the fix the texts in ISO publication may not back with relevant working URLs.

• See The RDFs should only go to second-level version spdx-3-model#1046 (ISO issue)

[bact]

Example validation failed because none of these URLs exist:

• https://spdx.org/schema/3.1/spdx-json-schema.json
• https://spdx.org/rdf/3.1/spdx-model.ttl
• https://spdx.org/rdf/3.1/spdx-context.jsonld

[goneall]

We need to upload the schema and context files to the website before we can merge this.

[bact]

Example validation failed because none of these URLs exist:

* https://spdx.org/schema/3.1/spdx-json-schema.json
* https://spdx.org/rdf/3.1/spdx-model.ttl
* https://spdx.org/rdf/3.1/spdx-context.jsonld

All of these URLs are now online.
But since currently they are redirected to actual copies at https://spdx.github.io/spdx-spec/v3.1-RC1/... they will still use SemVer from v3.1-RC1, which require "major.minor.patch" specVersion and will failed with the example that uses "major.minor" version (see the run log, line 34)