Apply make_aware when the original file contains actual datetimes

[vanschelven]

...rather than strings

Fix #1165

[coveralls]

Coverage increased (+0.002%) to 98.396% when pulling 8f96cfc on vanschelven:fix-datetime-use-tz into 2c1dac5 on django-import-export:main.

[matthewhegarty]

Please can you add a unit test to prove that your change solves the issue.
Also you can close the duplicate PR, we'll merge this change into the release 3 branch once it's gone into main.
thanks

[matthewhegarty]

hi @vanschelven Thanks so much for reporting and fixing this issue, it has been around for a while so it is great to get it resolved. I hope you don't mind but I refactored slightly to remove some minor duplication. See what you think. If you are OK with it I will merge soon.

[vanschelven]

LGTM