Fix for product of `Dirichlet` #658

Job	Run time
test (1.6, ubuntu-latest, x64, ForwardDiff)	6m 35s
test (1.6, ubuntu-latest, x64, Tracker)	6m 33s
test (1.6, ubuntu-latest, x64, ReverseDiff)	6m 47s
test (1.6, ubuntu-latest, x64, Zygote)	7m 36s
test (1.6, macOS-latest, x64, ForwardDiff)	6m 25s
test (1.6, macOS-latest, x64, Tracker)	6m 41s
test (1.6, macOS-latest, x64, ReverseDiff)	6m 29s
test (1.6, macOS-latest, x64, Zygote)	9m 0s
test (1, ubuntu-latest, x64, Enzyme)	7m 54s
test (1, ubuntu-latest, x64, ForwardDiff)	6m 22s
test (1, ubuntu-latest, x64, Tapir)	8m 48s
test (1, ubuntu-latest, x64, Tracker)	5m 58s
test (1, ubuntu-latest, x64, ReverseDiff)	6m 20s
test (1, ubuntu-latest, x64, Zygote)	6m 53s
test (1, macOS-latest, x64, Enzyme)	8m 37s
test (1, macOS-latest, x64, ForwardDiff)	6m 42s
test (1, macOS-latest, x64, Tapir)	10m 18s
test (1, macOS-latest, x64, Tracker)	8m 15s
test (1, macOS-latest, x64, ReverseDiff)	7m 51s
test (1, macOS-latest, x64, Zygote)	7m 50s
	2h 27m 54s

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