Type mismatch between open_mfdataset and open_virtual_mfdataset

[jbusecke]

Separating this out into its own issue.

Wondering if the dtype mismatch could be due to this deactivation of some CF to Codecs logic.

Originally posted by @jbusecke in #196

[maxrjones]

I think this may have been solved by zarr-developers/VirtualiZarr#845