Update Minimum supported dependencies workflow to allow for UserWarnings to be caught

[matthewfeickert]

This will require an update to

pyhf/.github/workflows/lower-bound-requirements.yml

Lines 35 to 42 in f7e974f

	- name: Test with pytest
	run: |
	# Override the ini option for filterwarnings with an empty list to disable error on filterwarnings
	# as testing for oldest releases that work with latest API, not the oldest releases that are warning
	# free. Though still show warnings by setting warning control to 'default'.
	export PYTHONWARNINGS='default'
	# Run on tests/ to skip doctests of src given examples are for latest APIs
	pytest --override-ini filterwarnings= --ignore tests/benchmarks/ --ignore tests/contrib --ignore tests/test_notebooks.py tests/

given that the current workflow ignores all warnings, and so this fails for the Minimum supported dependencies workflow. Do this in another PR.

$ PYTHONWARNINGS='default' pytest tests/test_infer.py

works, but I don't think that will work for the entire test suite.

Originally posted by @matthewfeickert in #1274 (comment)

[matthewfeickert]

Just get rid of the UserWarning instead #1274 (comment) as they aren't very useful in reality.