Fix Op(unflatten) (#2070) #8748

Job	Run time
build_docs (ubuntu-latest)	3m 2s
build_docs (windows-latest)	5m 18s
test (ubuntu-latest, py312)	17m 32s
update_readme	7s
test (ubuntu-latest, py311)	15m 56s
test (ubuntu-latest, py311-torch-nightly)	15m 24s
test (ubuntu-latest, py311-onnx-weekly)	15m 21s
test (ubuntu-latest, py311-ort-nightly)	16m 22s
test (ubuntu-latest, py310)	3m 44s
test (windows-latest, py312)	4m 19s
test (windows-latest, py311)	3m 58s
test (windows-latest, py311-torch-nightly)	3m 13s
test (windows-latest, py311-onnx-weekly)	4m 10s
test (windows-latest, py311-ort-nightly)	4m 11s
test (windows-latest, py310)	4m 6s
test (macos-latest, py312)	6m 50s
test (macos-latest, py311)	7m 40s
test (macos-latest, py311-torch-nightly)	7m 43s
test (macos-latest, py311-onnx-weekly)	8m 44s
test (macos-latest, py311-ort-nightly)	9m 43s
test (macos-latest, py310)	20m 30s
	2h 57m 53s

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