Full migration to idiomatic pytest #1046

Job	Run time
bugwarrior-multiarch-test (ppc64le)	9m 26s
bugwarrior-test (3.11)	30s
bugwarrior-test (3.12)	34s
bugwarrior-development-pip-test	48s
bugwarrior-test (3.13)	44s
bugwarrior-test (3.14)	40s
	12m 42s

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