[trainer] Fixes Typo in Predict Method of Trainer

[bhadreshpsavani]

What does this PR do?

Fixes typo in Predict Method of Trainer. This will enable saving files with the correct prefix test in Predict stage. Earlier it was saving it with the eval prefix for both predict and evaluate stage.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? This is discussed in [examples] should all examples support the predict stage? #10482
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Who can review?:

@stas00 @sgugger

[stas00]

Thank you for noticing this issue and providing a fix, @bhadreshpsavani

[sgugger]

LGTM, thanks a lot!