a possible bug in function find_mismatched_keys
Author: Yangr116
Pull request: yes

# What does this PR do?

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### Issue
When setting ```ignore_mismatched_sizes=True``` in ```Blip2ForConditionalGeneration```,  a KeyError is raised. 

### Reproduce
* blip2-flan-t5-xl
```
from transformers import Blip2ForConditionalGeneration

model_name = "Salesforce/blip2-flan-t5-xl" 
model = Blip2ForConditionalGeneration.from_pretrained(model_name, ignore_mismatched_sizes=True)
```
the output is ```KeyError: 'language_model.decoder.block.0.layer.2.DenseReluDense.wi_1.weight'```

* blip2-opt-2.7b
```
from transformers import Blip2ForConditionalGeneration

model_name = "Salesforce/blip2-opt-2.7b" 
model = Blip2ForConditionalGeneration.from_pretrained(model_name, ignore_mismatched_sizes=True)
```
the output is ```KeyError: 'language_model.lm_head.weight'```

Fixes #22563 (issue)



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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_22564). All of your documentation changes will be reflected on that endpoint.

cc @younesbelkada 
This is not the right fix as `loaded_keys` should only contain keys that are in the `state_dict` and we are looping other that in this piece of code.

In line [3054-3061](https://github.com/huggingface/transformers/blob/11fd2c773b11c3fcfe0fa25aa4b92db03c83636c/src/transformers/modeling_utils.py#L3054-L3061), the ```original_loaded_keys``` is input to the inner function ```_find_mismatched_keys```.

By using ```python -m pdb xxx.py```,  I found that some keys in ```original_loaded_keys ``` are not in the ```state_dict``` . 
So, in the line [2977](https://github.com/huggingface/transformers/blob/11fd2c773b11c3fcfe0fa25aa4b92db03c83636c/src/transformers/modeling_utils.py#L2977) , a ```KeyError``` is raised.


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