Fixes error raised when using multiple files for fields with no time dimension #619

Job	Run time
mypy	27s
py3.13 \| macos \| integration tests	28s
py3.13 \| macos \| unit tests	25s
py3.13 \| ubuntu \| integration tests	27s
py3.13 \| ubuntu \| unit tests	25s
py3.13 \| windows \| integration tests	24s
py3.13 \| windows \| unit tests	23s
py3.10 \| ubuntu \| integration tests	27s
py3.10 \| ubuntu \| unit tests	25s
py3.11 \| ubuntu \| unit tests	24s
py3.12 \| ubuntu \| unit tests	25s
merge-test-artifacts	1s
	4m 41s

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