Fix AttributeError on ManyToOneRel fields (#575)

[amureki]

Describe the change
Adds a defensive check to skip ForeignObjectRel instances (reverse relations like ManyToOneRel) in _skip_field().
These objects don't have has_default() and other Field attributes, which can cause AttributeError in certain model configurations.

I could not yet reproduce the issue with test models, this is why tests are a bit convoluted. Will follow up on this one.

PR Checklist

• Change is covered with tests
• CHANGELOG.md is updated if needed

Summary by CodeRabbit

• Bug Fixes
  • Fixed an AttributeError that occurred when processing models with reverse ForeignKey relations when optional field population was enabled.

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[coderabbitai]

📝 Walkthrough

Walkthrough

This PR fixes an AttributeError when processing Django models with reverse ForeignKey relations (ManyToOneRel) by implementing logic to properly identify and skip these fields during model baking, along with corresponding regression test coverage.

Changes

Cohort / File(s)	Summary
Documentation CHANGELOG.md	Added entry documenting the fix for AttributeError when processing models with reverse ForeignKey relations (issue #575).
Core Logic model_bakery/baker.py	Imported ForeignObjectRel and modified Baker._skip_field to identify and skip reverse relation fields, ensuring they are not treated as regular fields during baking.
Test Coverage tests/test_baker.py	Added TestReverseRelations class with a regression test that verifies _skip_field correctly returns True for reverse relations when fill_optional is enabled.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A rabbit hops through relations so fine,
Skipping reverse links in code so divine,
No AttributeError shall cross our path,
With ManyToOneRel we've fixed the wrath! 🌟

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Fix AttributeError on ManyToOneRel fields (#575)' directly and clearly describes the main fix implemented in this PR: addressing an AttributeError issue specifically with ManyToOneRel (reverse relation) fields.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch 575/attribute-error-many-to-one-rel

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