Issue in timestamp_compare when dates don't have the same length

[Darkheir]

When the length of modified is longer than created we may have the error "modified must be later than or equal to 'created'" even if it shouldn't.

The following example

{
    "id": "relationship--f9b5237e-cdbf-4aab-95e7-636d76716afd",
    "type": "relationship",
    "source_ref": "indicator--62b9046a-ec6f-43e1-a2dd-4b1fde63c7c5",
    "target_ref": "malware--0401b037-c8e1-4316-a107-e2af82b0e7b9",
    "relationship_type": "indicates",
    "spec_version": "2.1",
    "created": "2021-06-10T16:00:42.70954Z",
    "modified": "2021-06-10T16:00:42.709546Z"
}

Gives:

'modified' (2021-06-10T16:00:42.709546Z) must be later than or equal to 'created' (2021-06-10T16:00:42.70954Z)