Work around eachslice limitation on Julia <v1.9 #656

Job	Run time
test (1.6, ubuntu-latest, x64, ForwardDiff)	6m 34s
test (1.6, ubuntu-latest, x64, Tracker)	6m 18s
test (1.6, ubuntu-latest, x64, ReverseDiff)	6m 54s
test (1.6, ubuntu-latest, x64, Zygote)	7m 52s
test (1.6, macOS-latest, x64, ForwardDiff)	6m 29s
test (1.6, macOS-latest, x64, Tracker)	6m 14s
test (1.6, macOS-latest, x64, ReverseDiff)	7m 17s
test (1.6, macOS-latest, x64, Zygote)	7m 30s
test (1, ubuntu-latest, x64, Enzyme)	7m 58s
test (1, ubuntu-latest, x64, ForwardDiff)	6m 30s
test (1, ubuntu-latest, x64, Tapir)	8m 33s
test (1, ubuntu-latest, x64, Tracker)	6m 8s
test (1, ubuntu-latest, x64, ReverseDiff)	6m 22s
test (1, ubuntu-latest, x64, Zygote)	6m 45s
test (1, macOS-latest, x64, Enzyme)	8m 35s
test (1, macOS-latest, x64, ForwardDiff)	8m 6s
test (1, macOS-latest, x64, Tapir)	9m 3s
test (1, macOS-latest, x64, Tracker)	7m 57s
test (1, macOS-latest, x64, ReverseDiff)	8m 19s
test (1, macOS-latest, x64, Zygote)	8m 14s
	2h 27m 38s

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