Fix tests for Python 3.8 #521

Job	Run time
test-repositories-plus (3.8)	38s
test-repositories (3.8, zenodo)	19m 19s
test-repositories-plus (3.12)	36s
test-repositories (3.8, dataverse)	41s
test-api (3.8)	29s
test-repositories (3.8, figshare)	25s
test-api (3.12)	28s
test-repositories (3.8, djehuty)	15s
test-repositories (3.8, dryad)	22s
test-repositories (3.8, osf)	37m 39s
test-repositories (3.8, mendeley)	20s
test-repositories (3.8, dataone)	21s
test-repositories (3.8, dspace)	19s
test-repositories (3.8, pangaea)	23s
test-repositories (3.8, github)	15s
test-repositories (3.12, zenodo)	19m 12s
test-repositories (3.12, dataverse)	30s
test-repositories (3.12, figshare)	22s
test-repositories (3.12, djehuty)	16s
test-repositories (3.12, dryad)	21s
test-repositories (3.12, osf)	38m 35s
test-repositories (3.12, mendeley)	29s
test-repositories (3.12, dataone)	24s
test-repositories (3.12, dspace)	21s
test-repositories (3.12, pangaea)	21s
test-repositories (3.12, github)	14s
	2h 3m 35s

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