Create conda env for sphinx #56

Job	Run time
build_linux (3.8)	2m 4s
build_linux (3.9)	3m 41s
build_linux (3.10)	3m 19s
build_windows (3.8)	13m 21s
build_windows (3.9)	13m 0s
build_windows (3.10)	5m 7s
test_linux (3.8, true, ubuntu-20.04)	1m 12s
test_linux (3.9, true, ubuntu-20.04)	1m 43s
test_linux (3.10, true, ubuntu-20.04)	1m 41s
upload_linux	0s
test_windows (3.8, false, windows-latest)	5m 57s
test_windows (3.9, false, windows-latest)	5m 58s
test_windows (3.10, false, windows-latest)	6m 5s
upload_windows	0s
	1h 3m 8s

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