Correct Logging of Eval metric to Tensorboard
# What does this PR do?

An empty dictionary ``eval_metrics`` was being logged, is replaced by ``eval_metric`` which is the output dictionary of ``metric.compute()``. Probably this was a typo in the code. 

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Fixes # (issue)


## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).


## Who can review?

@sgugger, @patil-suraj
_The documentation is not available anymore as the PR was closed or merged._<|||||>Actually `eval_metrics` is never used, could you delete this line and update the PR ? This will fix the failing test.
https://github.com/huggingface/transformers/blob/d3bd9ac72802c0a3d04c3c63739bcd8f0731b593/examples/flax/text-classification/run_flax_glue.py#L595