Stop polluting dev env with docs deps #131

Job	Run time
Run linters	39s
Type-check package	22s
Build docs & run doctests	34s
Verify dev env (ubuntu-latest)	19s
Verify dev env (windows-latest)	49s
Verify dev env (macos-latest)	25s
Tests on 3.8	1m 0s
Tests on 3.9	1m 0s
Tests on 3.10	1m 8s
Tests on 3.11	1m 2s
Tests on 3.12	1m 13s
Tests on pypy-3.8	1m 16s
Tests on pypy-3.9	1m 20s
Combine & check coverage	14s
required-checks-pass	2s
	11m 23s

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