docs linkcheck failing for SciPy conference proceedings

[matthewfeickert]

The linkcheck failure in the docs CI

pyhf/.github/workflows/docs.yml

Lines 62 to 65 in af5d952

	- name: Check for broken links
	run: |
	pushd docs
	make linkcheck

is due to the SciPy conference proceedings either being down or getting moved. I will track this on scipy-conference/conference.scipy.org#55.