Fix date time interface

[geek-merlin]

Description

Using Carbon, my serde broke. It serialized fine to the specified format, but deserialization throwed.

How has this been tested?

In my app i made an override with exactly this code, which fixed the issue for me.
I tried to add a meaningful test case.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING document.
• My pull request addresses exactly one patch/feature.
• I have created a branch for this patch/feature.
• Each individual commit in the pull request is meaningful.
• I have added tests to cover my changes.
• If my change requires a change to the documentation, I have updated it accordingly.

[Crell]

I really dislike what Carbon does. 😄 But this seems like a reasonable fix, and the test is valid, so merging.

Thanks!