AD fix for PDBijector #484

Job	Run time
test (1.6, ubuntu-latest, x64, ForwardDiff)	4m 46s
test (1.6, ubuntu-latest, x64, Tracker)	3m 41s
test (1.6, ubuntu-latest, x64, ReverseDiff)	4m 11s
test (1.6, ubuntu-latest, x64, Zygote)	4m 48s
test (1.6, macOS-latest, x64, ForwardDiff)	4m 44s
test (1.6, macOS-latest, x64, Tracker)	4m 37s
test (1.6, macOS-latest, x64, ReverseDiff)	5m 3s
test (1.6, macOS-latest, x64, Zygote)	5m 33s
test (1, ubuntu-latest, x64, ForwardDiff)	3m 51s
test (1, ubuntu-latest, x64, Tracker)	4m 58s
test (1, ubuntu-latest, x64, ReverseDiff)	4m 58s
test (1, ubuntu-latest, x64, Zygote)	4m 52s
test (1, macOS-latest, x64, ForwardDiff)	4m 57s
test (1, macOS-latest, x64, Tracker)	5m 37s
test (1, macOS-latest, x64, ReverseDiff)	4m 43s
test (1, macOS-latest, x64, Zygote)	6m 9s
	1h 17m 28s

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