Update mimalloc to 3.2.6 #69

Job	Run time
build (windows-latest, windows, win32-x64)	5m 29s
build (macos-latest, darwin, darwin-arm64)	4m 56s
build (macos-latest, darwin, darwin-x64)	2m 25s
build (ubuntu-latest, linux, linux-x64)	2m 48s
	15m 38s

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