tf.keras.metrics.get return string intead of exception
Hi **@venergiac-bh** 
I replicated this issue with Tf 2.14 ,2.13 and tf-nightly too. I attached a [gist](https://colab.research.google.com/gist/Venkat6871/0ebdf8b84d6ab18e13df7188fc821346/62345_2-14-v.ipynb) here for reference.

Thank you!  Hi @venergiac-bh ,

I have tested it with keras-nightly(3.0.0.dev2023110803) and it is raising intended exception. Please refer attached [gist](https://colab.sandbox.google.com/gist/SuryanarayanaY/36958e240b0ecb9583f86d19df361a73/62345.ipynb#scrollTo=41bcOz8UCedO). This issue is stale because it has been open for 7 days with no activity. It will be closed if no further activity occurs. Thank you. This issue was closed because it has been inactive for 7 days since being marked as stale. Please reopen if you'd like to work on this further. Are you satisfied with the resolution of your issue?
<a href="https://docs.google.com/forms/d/e/1FAIpQLSfaP12TRhd9xSxjXZjcZFNXPGk4kc1-qMdv3gc6bEP90vY1ew/viewform?entry.85265664=Yes&entry.2137816233=https://github.com/tensorflow/tensorflow/issues/62345">Yes</a>
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### Issue type

Bug

### Have you reproduced the bug with TensorFlow Nightly?

No

### Source

binary

### TensorFlow version

2.14.0

### Custom code

No

### OS platform and distribution

Windows

### Mobile device

_No response_

### Python version

3.10

### Bazel version

_No response_

### GCC/compiler version

_No response_

### CUDA/cuDNN version

_No response_

### GPU model and memory

_No response_

### Current behavior?

Problem on metrics `keras.metrics.get`; it should raise an exception if metric doesn't exist: InvalidIdentifier

### Standalone code to reproduce the issue

```shell
Problem on metrics

         import tensorflow as tf
         tf.keras.metrics.get('abc')

it returns "abc", but as per documentation it should raise an exception ValueError
```


### Relevant log output

_No response_