Fix `dim_zero_cat` reduction #6526

Job	Run time
check-code / mypy	1m 45s
check-code / pre-commit	39s
check-schema / schema	11s
check-md-links / markdown-link-check	3m 45s
check-package / init-store	6s
check-package / pkg-build (ubuntu-latest)	25s
check-package / pkg-check (ubuntu-20.04, 3.8)	2m 34s
check-package / pkg-check (ubuntu-20.04, 3.10)	1m 1s
check-package / pkg-check (macos-11, 3.8)	2m 16s
check-package / pkg-check (macos-11, 3.10)	2m 6s
check-package / pkg-check (windows-2022, 3.8)	2m 47s
check-package / pkg-check (windows-2022, 3.10)	2m 36s
check-package / pkg-guardian	1s
	20m 12s

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