Include slow unit tests in CI #538

Job	Run time
Measure coverage	28m 23s
miri	4m 25s
Additional Builds and Concurrency Tests	13m 7s
Basic Checks	20m 0s
Release builds and tests	9m 29s
sanitize (address)	17m 31s
Slow tests	18m 29s
sanitize (address, multi-threading)	17m 47s
sanitize (leak)	8m 9s
sanitize (leak, multi-threading)	8m 3s
	2h 25m 23s

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