docs: fix graphs on RTD #195

Job	Run time
Tests on paywalled platforms (macos-13-xlarge, 3.12)	50s
Tests on other platforms (windows-2019, 3.10)	3m 3s
Tox test (py38)	2m 6s
Tests on other platforms (windows-2022, 3.11)	2m 40s
Tox test (py39)	2m 2s
Tests on other platforms (windows-2022, 3.12)	2m 35s
Tox test (py310)	1m 56s
Tests on other platforms (macos-12, 3.11)	1m 39s
Tox test (py311)	2m 12s
Tests on other platforms (macos-13, 3.12)	1m 52s
Tox test (py312-cover)	3m 0s
Tox test (docs, graphviz)	1m 52s
Docker image	0s
PyPI packaging	0s
	25m 47s

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