Fix typo in gitignore

[astralcai]

Jupyter notebooks end with .ipynb, not .ipynp.

[github-actions[bot]]

Hello. You may have forgotten to update the changelog! Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.66%. Comparing base (d65f671) to head (3b74887). Report is 254 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5834 +/- ## ========================================== - Coverage 99.66% 99.66% -0.01% ========================================== Files 415 417 +2 Lines 39824 39682 -142 ========================================== - Hits 39692 39549 -143 - Misses 132 133 +1 ```

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