Reverting testing with Python 3.12 due to pydantic error via kg-core:

```
fairgraph/__init__.py:22: in <module>
    from .client import KGClient
fairgraph/client.py:28: in <module>
    from kg_core.kg import kg
/opt/hostedtoolcache/Python/3.12.6/x64/lib/python3.12/site-packages/kg_core/kg.py:32: in <module>
    from kg_core.response import Result, Instance, JsonLdDocument, ResultsById, ResultPage, ReleaseStatus, Error, translate_error, User, Scope, SpaceInformation, TypeInformation, TermsOfUse, ListOfUUID, ListOfReducedUserInformation
/opt/hostedtoolcache/Python/3.12.6/x64/lib/python3.12/site-packages/kg_core/response.py:83: in <module>
    class Scope(BaseModel):
/opt/hostedtoolcache/Python/3.12.6/x64/lib/python3.12/site-packages/pydantic/main.py:286: in __new__
    cls.__try_update_forward_refs__()
/opt/hostedtoolcache/Python/3.12.6/x64/lib/python3.12/site-packages/pydantic/main.py:808: in __try_update_forward_refs__
    update_model_forward_refs(cls, cls.__fields__.values(), cls.__config__.json_encoders, localns, (NameError,))
/opt/hostedtoolcache/Python/3.12.6/x64/lib/python3.12/site-packages/pydantic/typing.py:554: in update_model_forward_refs
    update_field_forward_refs(f, globalns=globalns, localns=localns)
/opt/hostedtoolcache/Python/3.12.6/x64/lib/python3.12/site-packages/pydantic/typing.py:520: in update_field_forward_refs
    field.type_ = evaluate_forwardref(field.type_, globalns, localns or None)
/opt/hostedtoolcache/Python/3.12.6/x64/lib/python3.12/site-packages/pydantic/typing.py:66: in evaluate_forwardref
    return cast(Any, type_)._evaluate(globalns, localns, set())
E   TypeError: ForwardRef._evaluate() missing 1 required keyword-only argument: 'recursive_guard'
```

.github/workflows/tests.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+        python-version: ["3.8", "3.9", "3.10", "3.11"]
 
     steps:
       - uses: actions/checkout@v4