Stop using patched fork for sphinx-polyversion

[ziw-liu]

Test if real-yfprojects/sphinx-polyversion#42 fixes the need for:

iohub/.github/workflows/docs.yml

Lines 34 to 35 in 431d74b

	# temporary fix for sphinx-polyversion
	pip install --force-reinstall git+https://github.com/ziw-liu/sphinx-polyversion.git@iohub-staging