Fix audit finding F15: Reconcile dependency pinning (jsonschema==4.26.0) in pyproject.toml.
Recorded from user prompt in conversation 78d87a8b-d52c-4b44-b8f5-077656700b95.
pyproject.tomljsonschema==4.26.0 to match runtime validator requirements.python -m data2dsl_contract_v0.validate --self-test: passed.