Fix `segmentation.MeanIoU` #9051

Job	Run time
check-schema / schema	13s
check-code / mypy	2m 17s
check-md-links / markdown-link-check	14s
check-package / init-store	4s
check-package / pkg-build (ubuntu-latest)	17s
check-package / pkg-check (ubuntu-22.04, 3.8)	2m 46s
check-package / pkg-check (ubuntu-22.04, 3.11)	2m 26s
check-package / pkg-check (macos-12, 3.8)	1m 41s
check-package / pkg-check (macos-12, 3.11)	1m 42s
check-package / pkg-check (windows-2022, 3.8)	2m 49s
check-package / pkg-check (windows-2022, 3.11)	3m 39s
check-package / pkg-guardian	1s
	18m 9s

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