Create conda env for sphinx (#47) #38

Job	Run time
build_linux (3.8)	5m 50s
build_windows (3.8)	12m 36s
build_linux (3.9)	11m 30s
build_windows (3.9)	12m 20s
build_linux (3.10)	8m 48s
build_windows (3.10)	10m 46s
test_linux (3.8, true, ubuntu-20.04)	2m 30s
test_linux (3.9, true, ubuntu-20.04)	2m 37s
test_linux (3.10, true, ubuntu-20.04)	1m 45s
test_windows (3.8, false, windows-latest)	7m 40s
test_windows (3.9, false, windows-latest)	4m 55s
test_windows (3.10, false, windows-latest)	6m 48s
upload_linux (3.8)	32s
upload_linux (3.9)	19s
upload_linux (3.10)	16s
upload_windows (3.8)	1m 42s
upload_windows (3.9)	1m 40s
upload_windows (3.10)	1m 40s
	1h 34m 14s

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