fix: adapt fixture usage to newer pytest versions #158

Job	Run time
test (differential_gene_expression.ipynb)	1m 20s
test (distance_tests.ipynb)	1m 22s
test (guide_rna_assignment.ipynb)	1m 10s
test (milo.ipynb)	1m 8s
test (cinemaot.ipynb)	1m 7s
test (enrichment.ipynb)	1m 22s
test (distances.ipynb)	1m 20s
test (sccoda.ipynb)	1m 10s
test (mixscape.ipynb)	1m 8s
test (augur.ipynb)	1m 8s
	12m 15s

Provide feedback