Adding a test to prove that the `DurationField` is not stored as an `int` and that that causes issues.
Adding a test to prove that the `DurationField` is not stored as an `int` and that that causes issues.

#512

armirusco/djangae,potatolondon/djangae,asendecka/djangae,grzes/djangae,kirberich/djangae,kirberich/djangae,potatolondon/djangae,kirberich/djangae,asendecka/djangae,armirusco/djangae,armirusco/djangae,grzes/djangae,asendecka/djangae,grzes/djangae