Notebook bug fixes
Signed-off-by: Virginia Adams <vadams@nvidia.com>

Fixes Entity Linking and Prompt Learning Notebook Bugs:
https://nvbugs/3802936 [ML-NeMo][A40] Entity_Linking_Medical.ipynb failed with TypeError: __init__() got an unexpected keyword argument 'checkpoint_callback'
https://nvbugs/3801562 [ML-NeMo][A40] Multitask_Prompt_and_PTuning.ipynb contains broken links
https://nvbugs/3803232 [ML-NeMo][A40] Multitask_Prompt_and_PTuning.ipynb failed with FileNotFoundError: [Errno 2] No such file or directory: 'data/SQuAD/train-v1.1.json'

**Collection**: NLP

# Changelog 
- Updates entity linking and prompt learning notebooks

# Usage
N/A

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**PR Type**:
- [ ] New Feature
- [x] Bugfix
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# Additional Information
* Related to # (issue)
