Fix typo in pandas_support.ipynb

[edouardberthe]

• [ ] Closes # (insert issue number)
• [ ] Executed pre-commit run --all-files with no errors
• [ ] The change is fully covered by automated unit tests
• [ ] Documented in docs/ as appropriate
• [ ] Added an entry to the CHANGES file

[andrewgsavage]

ty for submitting this fix. I didn't merge as there's a few more fixes in the pint one which has been copied over in https://github.com/hgrecco/pint-pandas/pull/105