Fixes error raised when using multiple files for fields with no time dimension #620

Job	Run time
py3.13 \| macos \| unit tests	10m 20s
mypy	3m 26s
py3.13 \| ubuntu \| unit tests	13m 44s
py3.13 \| macos \| integration tests	12m 49s
py3.13 \| windows \| unit tests	19m 44s
py3.13 \| ubuntu \| integration tests	29m 10s
py3.13 \| windows \| integration tests	49m 6s
py3.10 \| ubuntu \| unit tests	13m 44s
py3.10 \| ubuntu \| integration tests	18m 48s
py3.11 \| ubuntu \| unit tests	13m 23s
py3.12 \| ubuntu \| unit tests	14m 16s
merge-test-artifacts	4s
	3h 18m 34s

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