Remove six #1122

Job	Run time
Run tests with different pydantic versions	3m 41s
Run tests with coverage	2m 58s
Run tests (3.8)	2m 0s
Run linters (flake8)	1m 53s
Run tests on legacy versions (3.7)	2m 12s
Run tests (3.9)	2m 16s
Run linters (pydocstyle)	1m 48s
Run tests (3.10)	2m 9s
Run linters (mypy)	1m 59s
Run tests (3.11)	2m 1s
Run linters (pylint)	1m 50s
Run tests (3.12)	2m 1s
Run tests (3.13)	2m 8s
	28m 56s

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