Create conda env for sphinx #35

Job	Run time
build_linux (3.8)	5m 37s
build_linux (3.9)	8m 49s
build_linux (3.10)	5m 44s
build_windows (3.8)	12m 49s
build_windows (3.9)	12m 1s
build_windows (3.10)	11m 40s
test_linux (3.8, true, ubuntu-20.04)	3m 28s
test_linux (3.9, true, ubuntu-20.04)	2m 51s
test_linux (3.10, true, ubuntu-20.04)	2m 12s
upload_linux	0s
test_windows (3.8, false, windows-latest)	8m 27s
test_windows (3.9, false, windows-latest)	8m 51s
test_windows (3.10, false, windows-latest)	5m 18s
upload_windows	0s
	1h 27m 47s

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