Specify type for the string literals defined in the individuals

[goneall]

Pyshacl is failing validation due to the type not being xsd:string for the comment fields defined in the creationInfo individuals.

For example:

ns1:comment "This individual element was defined by the spec."@en ;

should be changed to:

ns1:comment "This individual element was defined by the spec."^^xsd:string ;

Reference spdx/spdx-3-model#936 (comment).

[zvr]

Grrr... stupid typo, instead of it being rdfs:comment it's a ns1:comment (so in SPDX namespace).
I'll fix it.

[bact]

Warn that "ns1" "ns2" etc namespaces are up to rdflib to decided and this order could be changed if the code is updated (for example, we refactor the code or we have new profile).

Maybe in the next version (3.1?), we may like to suggest a namespace for each of the Profile and use than in RDF generation:

• Specify spdx prefix names in model Turtle file ("@prefix ns2" -> "@prefix spdx-sw") #157