[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 https://github.com/spdx/spdx-3-model/issues/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 https://github.com/spdx/spdx-3-model/issues/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