Challenge_pk and phase_pk change type from string to int when resubmitting

Hello everyone,
while processing submissions for a challenge, I noticed that the `phase_pk` and `challenge_pk` keys change type.
When a submission is sent the first time, my evaluation script receives them as a `string`, e.g.
```
b'{"body":{"challenge_pk":"1134","phase_pk":"2326","is_static_dataset_code_upload_submission":false," ....
```
However, if the submission is resent again by clicking on "Rerun submission" on EvalAI All submissions tab, the `challenge_pk` and `phase_pk` become `int` type:
```
b'{"body":{"challenge_pk":1134,"phase_pk":2326,"submission_pk":154550,"is_static...
```

I discovered this as my evaluation script had to do different things depending on the `phase_pk` and having it change from `string` to `int` raised an exception.