Fix up pint serialisation

[znichollscr]

Description

Checklist

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Changelog item added to changelog/

[codecov]

Codecov Report

Attention: Patch coverage is 94.73684% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 96.22%. Comparing base (911b55c) to head (38a385c).

❗ Current head 38a385c differs from pull request most recent head 0da952e. Consider uploading reports for the commit 0da952e to get more accurate results

Files	Patch %	Lines
src/pydoit_nb/config_handling.py	90.90%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #9      +/-   ##
==========================================
- Coverage   96.29%   96.22%   -0.08%     
==========================================
  Files          16       16              
  Lines         486      503      +17     
  Branches       80       83       +3     
==========================================
+ Hits          468      484      +16     
  Misses         18       18              
- Partials        0        1       +1     

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