Fix test for ExperimentExplorer daterange
Fix test for ExperimentExplorer daterange

This was previously space-padding a 3-digit year, however it seems
that some change to cftime has caused it to now zero-pad the year.
The rest of the ExperimentExplorer should still work with this change,
but we just need to update the test to not throw an incorrect assert.

OceansAus/cosima-cookbook