Disable jemalloc on mac #4869

Job	Run time
Basic Checks	17m 52s
sanitize (address)	13m 41s
Release builds and tests	13m 5s
sanitize (address, multi-threading)	12m 30s
Additional Builds and Concurrency Tests	12m 20s
sanitize (leak)	5m 51s
Slow tests	7m 48s
sanitize (leak, multi-threading)	5m 49s
Measure coverage	16m 28s
miri	2m 56s
	1h 48m 20s

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