fix: Ensure eval mode for TableReader model for predictions

[sjrl]

Related Issues

• fixes N/A

Proposed Changes:

I added a call to make sure to set the TableReader model to eval mode when running a prediction. Otherwise, currently, if the model is set to train mode the predictions become random due to layers like BatchNorm and dropout being present in the underlying model architecture. This is something we already do for some of our nodes like the DensePassageRetriever.

How did you test it?

I added a new unit test to make sure everything works. I did confirm that this unit test fails without the new changes.

Notes for the reviewer

This probably was not noticed before because the model is set to eval mode by default when loading it.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added tests that demonstrate the correct behavior of the change
• I've used the conventional commit convention for my PR title
• I documented my code
• I ran pre-commit hooks and fixed any issue

[vblagoje]

LGTM @sjrl