fix pydantic #190

Job	Run time
lint (flake8)	20s
lint (mypy)	2m 52s
lint (black)	20s
test api	4m 17s
lint (pydocstyle)	0s
test-headers	4m 26s
test-no-engine	4m 6s
test-clean-install-ubuntu	0s
test-internals	0s
test-clean-install-windows	0s
test-asv-benchmarks	0s
test-ubuntu (engine unidist ${{ matrix.unidist-backend }}, python ${{ matrix.python-version }})	0s
Test ${{ matrix.execution }} execution, Python 3.8	0s
Test HDK storage format, Python 3.8	0s
test cloud	0s
test experimental	0s
test-ubuntu (engine ${{ matrix.engine }}, python ${{ matrix.python-version }}, ${{ matrix.test_task }})	0s
test (pyarrow, python ${{ matrix.python-version }})	0s
test-windows (engine ${{ matrix.engine }}, python ${{ matrix.python-version }}, ${{ matrix.test_task }})	0s
test-spreadsheet (engine ${{ matrix.engine }}, python ${{ matrix.python-version }})	0s
upload-coverage	0s
	16m 21s

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