fix: Update related objects with unique_together

[zvyn]

Description

Resolves the issue described in #360: Support updating related objects with unique_together on the foreign key where the data identifies a single object in the database.

Types of Changes

• Bugfix
• Enhancement/optimization

Issues Fixed or Closed by This PR

• Updating related objects with unique_together including the FK raises IntegrityError #360

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[codecov-commenter]

Codecov Report

Patch coverage: 66.66% and no project coverage change.

Comparison is base (4cde249) 87.99% compared to head (9f01759) 87.99%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #362   +/-   ##
=======================================
  Coverage   87.99%   87.99%           
=======================================
  Files          33       33           
  Lines        2940     2941    +1     
=======================================
+ Hits         2587     2588    +1     
  Misses        353      353           

Files Changed	Coverage Δ
strawberry_django/mutations/resolvers.py	87.05% <66.66%> (+0.05%)	⬆️

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[bellini666]

LGTM 👍🏼

Thank you for this :)