docs: don't repeat top-level dependencies #178

Job	Run time
Tests on paywalled platforms (macos-13-xlarge, 3.12)	48s
Tests on other platforms (windows-2019, 3.10)	2m 56s
Tox test (py38)	2m 8s
Tests on other platforms (windows-2022, 3.11)	3m 1s
Tox test (py39)	2m 3s
Tests on other platforms (windows-2022, 3.12)	2m 48s
Tox test (py310)	2m 7s
Tests on other platforms (macos-12, 3.11)	1m 38s
Tox test (py311)	2m 0s
Tests on other platforms (macos-13, 3.12)	2m 8s
Tox test (py312-cover)	3m 10s
Tox test (docs, graphviz)	2m 4s
Docker image	0s
PyPI packaging	0s
	26m 51s

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