Fix/peft flattening typo
Author: leaderofARS
Pull request: yes

# What does this PR do?                                                                                                                                  
                                                                                                                                                             
This PR corrects a minor spelling typo in the PEFT integration error messages. Specifically, it corrects the misspelling of "flattening operation" (previously written as "flatteing operatio") in two `NotImplementedError` messages within `src/transformers/integrations/peft.py` to improve clarity.      
                                                                                                                                                             
## Code Agent Policy                                                                                                                                     
                                                                                                                                                             
- [x] I confirm that this is not a pure code agent PR.                                                                                                   
                                                                                                                                                             
## Before submitting                                                                                                                                     
- [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).                                                   
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#create-a-pull-request), Pull Request section?                                                                                                                              
- [ ] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link                                 to it if that's the case.                                                                                                                          
- [ ] Did you make sure to update the documentation with your changes? Here are the                                                               [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and                                                       [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).                 
- [ ] Did you write any new necessary tests?                                                                                                             
                                                                                                                                                             
                                                                                                                                                             
## Who can review?                                                                                                                                       
                                                                                                                                                             
@BenjaminBossan 
@githubnemo 

Comments:
**[For maintainers]** Suggested jobs to run (before merge)

run-slow: higgs_audio_v2

View the CircleCI Test Summary for this PR:

https://huggingface.co/spaces/transformers-community/circle-ci-viz?pr=46537&sha=e7b3cc