Test inputs require a batch size of 1

[JonasHell]

Validation job fails with
'error': "Shape (8, 1, 256, 256) of test input 0 'input0' does not match input shape description: " 'ParametrizedInputShape(min=[1, 1, 32, 32], step=[0, 0, 16, 16]).',
even though these shapes are a valid combination.

(see bioimage-io/collection-bioimage-io#615
and https://github.com/bioimage-io/collection-bioimage-io/actions/runs/5596217298/job/15158187714#step:9:53)

As discussed with @FynnBe offline, test inputs are expected to have a batch size b=1 and therefore the job fails for b>1.

Potential solutions are to either allow test inputs with b>1 or to specify that b must be 1 and to adjust the error message accordningly.

[FynnBe]

this may have been fixed already. We need to test if this can still be reproduced