Float16 mixed precision training
@HLneoh 
In order to expedite the trouble-shooting process, please provide a code snippet to reproduce the issue reported here. Thank you! 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/61771">Yes</a>
<a href="https://docs.google.com/forms/d/e/1FAIpQLSfaP12TRhd9xSxjXZjcZFNXPGk4kc1-qMdv3gc6bEP90vY1ew/viewform?entry.85265664=No&entry.2137816233=https://github.com/tensorflow/tensorflow/issues/61771">No</a>

### Issue type

Bug

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

Yes

### Source

source

### TensorFlow version

2.13.0

### Custom code

Yes

### OS platform and distribution

Ubuntu 20.04.5 LTS

### Mobile device

_No response_

### Python version

Python 3.10.9

### Bazel version

_No response_

### GCC/compiler version

_No response_

### CUDA/cuDNN version

_No response_

### GPU model and memory

A6000

### Current behavior?

Enabled float16 training by setting the mixed precision policy, but why I still need to manually cast the y tensors to float16 before calculating the loss?


Error when no manual cast the tensor:
![image](https://github.com/tensorflow/tensorflow/assets/25906607/46c5efcb-f2c2-4b7a-9483-46656009071b)


### Standalone code to reproduce the issue

```shell
Confidential.
```


### Relevant log output

_No response_