Fix onnx export. #94

Job	Run time
test-unix-nightly (macos, 3.11, 12.1, nightly)	6m 1s
test-win-nightly (windows, 3.9, 12.1, nightly)	2m 35s
test-unix-nightly (linux, 3.11, 12.1, nightly)	3m 52s
test-stable (macos, 3.9, 12.1, stable)	5m 30s
test-win-nightly (windows, 3.10, 12.1, nightly)	2m 39s
test-win-nightly (windows, 3.11, 12.1, nightly)	2m 43s
test-stable (macos, 3.10, 12.1, stable)	5m 31s
test-win-nightly (windows, 3.12, 12.1, nightly)	2m 38s
test-stable (macos, 3.11, 12.1, stable)	5m 27s
test-stable (macos, 3.12, 12.1, stable)	5m 31s
test-stable (linux, 3.9, 12.1, stable)	4m 0s
test-stable (linux, 3.10, 12.1, stable)	3m 56s
test-stable (linux, 3.11, 12.1, stable)	4m 4s
test-stable (linux, 3.12, 12.1, stable)	3m 59s
test-stable (windows, 3.9, 12.1, stable)	2m 29s
test-stable (windows, 3.10, 12.1, stable)	2m 28s
test-stable (windows, 3.11, 12.1, stable)	2m 40s
test-stable (windows, 3.12, 12.1, stable)	2m 37s
	1h 8m 40s

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