temporary pin to pre-pydantic v2 gufe commit

[atravitz]

keep CI green until #1431 is merged.

Checklist

• Added a news entry

Developers certificate of origin

• I certify that this contribution is covered by the MIT License here and the Developer Certificate of Origin at https://developercertificate.org/.

[github-actions]

No API break detected ✅

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.17%. Comparing base (7584efe) to head (6cdc65b).
⚠️ Report is 118 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1533      +/-   ##
==========================================
- Coverage   95.23%   93.17%   -2.06%     
==========================================
  Files         172      172              
  Lines       14454    14454              
==========================================
- Hits        13765    13468     -297     
- Misses        689      986     +297     

Flag	Coverage Δ
fast-tests	93.17% <ø> (?)
slow-tests	?

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