CITATION.cff is not compliant with schema 1.3.0

[e-kwsm]

Now (b6045d7) I receive error different from #414, so I opened this issue separately.

$ cffconvert --validate --verbose --url https://github.com/citation-file-format/cffconvert
jsonschema.exceptions.ValidationError: {'type': 'doi', 'value': '10.5281/zenodo.5521767', 'description': 'Persistent identifier for this version of cffconvert', 'relation': 'isIdenticalTo'} is not valid under any of the given schemas

Failed validating 'oneOf' in schema['properties']['identifiers']['items']:
    {'description': 'An identifier for a work.',
     'oneOf': [{'additionalProperties': False,
                'properties': {'description': {'$ref': '#/$defs/identifier-description'},
                               'relation': {'$ref': '#/$defs/identifier-relation'},
                               'type': {'const': 'doi', 'type': 'string'},
                               'value': {'$ref': '#/$defs/doi'}},
                'required': ['type', 'value'],
                'type': 'object'},
               {'additionalProperties': False,
                'properties': {'description': {'$ref': '#/$defs/identifier-description'},
                               'relation': {'$ref': '#/$defs/identifier-relation'},
                               'type': {'const': 'url', 'type': 'string'},
                               'value': {'$ref': '#/$defs/url'}},
                'required': ['type', 'value'],
                'type': 'object'},
               {'additionalProperties': False,
                'properties': {'description': {'$ref': '#/$defs/identifier-description'},
                               'relation': {'$ref': '#/$defs/identifier-relation'},
                               'type': {'const': 'swh', 'type': 'string'},
                               'value': {'$ref': '#/$defs/swh-identifier'}},
                'required': ['type', 'value'],
                'type': 'object'},
               {'additionalProperties': False,
                'properties': {'description': {'$ref': '#/$defs/identifier-description'},
                               'relation': {'$ref': '#/$defs/identifier-relation'},
                               'type': {'const': 'other', 'type': 'string'},
                               'value': {'$ref': '#/$defs/strictish-string'}},
                'required': ['type', 'value'],
                'type': 'object'}]}

On instance['identifiers'][1]:
    {'type': 'doi',
     'value': '10.5281/zenodo.5521767',
     'description': 'Persistent identifier for this version of cffconvert',
     'relation': 'isIdenticalTo'}

cffconvert/CITATION.cff

Line 51 in b6045d7

relation: isPartOf

and

cffconvert/CITATION.cff

Line 55 in b6045d7

relation: isIdenticalTo

are not compliant with

cffconvert/src/cffconvert/schemas/1.3.0/schema.json

Line 507 in b6045d7

"IsPartOf",

and

cffconvert/src/cffconvert/schemas/1.3.0/schema.json

Line 502 in b6045d7

"IsIdenticalTo",

respectively.