Getting Pydantic serializer warnings when running MetaKB tests

[korikuzma]

Describe the bug

When running MetaKB tests, I'm getting the following:

metakb/venv/lib/python3.11/site-packages/pydantic/main.py:426: UserWarning: Pydantic serializer warnings:
    Expected `enum` but got `str` with value `'RxNorm'` - serialized value may not be as expected
    Expected `enum` but got `str` with value `'NCIt'` - serialized value may not be as expected
    Expected `enum` but got `str` with value `'HemOnc'` - serialized value may not be as expected
    Expected `enum` but got `str` with value `'DrugBank'` - serialized value may not be as expected
    Expected `enum` but got `str` with value `'GuideToPHARMACOLOGY'` - serialized value may not be as expected
    Expected `enum` but got `str` with value `'ChEMBL'` - serialized value may not be as expected
    Expected `enum` but got `str` with value `'ChemIDplus'` - serialized value may not be as expected
    Expected `enum` but got `str` with value `'Wikidata'` - serialized value may not be as expected

Steps to reproduce

In MetaKB, run transformers tests (python3 -m pytest tests/unit/transformers -vv). I'm currently using issue-240 branch, but could use staging too.

Expected behavior

I do not expect to see any Pydantic serializer warnings

Current behavior

I see Pydantic serializer warnings

Acceptance Criteria

Given I'm running MetaKB transformer tests,
When I see the warnings summary in the terminal,
Then I will not see any Pydantic serializer warnings

Possible reason(s)

source_matches has type dict[SourceName, MatchesNormalized], but it's actually be used as dict[str, MatchesNormalized]

Suggested fix

No response

Branch, commit, and/or version

v0.7.1

Screenshots

No response

Environment details

NA

Additional details

No response

Contribution

Yes, I can create a PR for this fix.