Update Hypothesis strategy to avoid producing cftime items #10907
Description
we didn't have hypothesis in the bare-minimum CI, which means those tests were skipped before.
What we could do to fix this is have the cftime strategy not produce any values if cftime is missing (or find some other way of skipping the generation of cftime datetime types if cftime is not installed). This should probably be its own PR, though.
Originally posted by @keewis in #10888 (comment)