Only-data dataset loaded unexpectedly as validation split
> "my_dataset_dev" doesn't match your regex, "my_dataset_validation" doesn't either ... Why not always "train" unless specified?

And `my_dataset_dev.foo` would match the pattern, and we also have the same pattern but for the "validation" keyword so `my_dataset_validation.foo` would work too
## Describe the bug
As reported by @thomasw21 and @lhoestq, a dataset containing only a data file whose name matches the pattern `*dev*` will be returned as VALIDATION split, even if this is not the desired behavior, e.g. a file named `datosdevision.jsonl.gz`.
Only-data dataset loaded unexpectedly as validation split 
 ## Describe the bug
As reported by @thomasw21 and @lhoestq, a dataset containing only a data file whose name matches the pattern `*dev*` will be returned as VALIDATION split, even if this is not the desired behavior, e.g. a file named `datosdevision.jsonl.gz`. 
 > "my_dataset_dev" doesn't match your regex, "my_dataset_validation" doesn't either ... Why not always "train" unless specified?

And `my_dataset_dev.foo` would match the pattern, and we also have the same pattern but for the "validation" keyword so `my_dataset_validation.foo` would work too