Remove six #1116

Job	Run time
Run tests on legacy versions (3.7)	2m 12s
Run tests with coverage	3m 4s
Run tests with different pydantic versions	3m 41s
Run linters (flake8)	1m 45s
Run tests (3.8)	1m 59s
Run linters (pydocstyle)	1m 53s
Run tests (3.9)	2m 4s
Run linters (mypy)	1m 55s
Run tests (3.10)	2m 7s
Run linters (pylint)	1m 50s
Run tests (3.11)	2m 2s
Run tests (3.12)	2m 0s
Run tests (3.13)	2m 11s
	28m 43s

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