Fix incorrect reference for renamed model associations

[jayelkaake]

What this does

Resolves unknown attribute 'model' for CustomMessageClass error which occurs when you try to use with_model on an ActiveRecord Chat class that has a custom Message class name using the acts_as.

It appears to be a small typo.

Type of change

• Bug fix
• New feature
• Breaking change
• Documentation
• Performance improvement

Scope check

• I read the Contributing Guide
• This aligns with RubyLLM's focus on LLM communication
• This isn't application-specific logic that belongs in user code
• This benefits most users, not just my specific use case

Quality check

• I ran overcommit --install and all hooks pass
• I tested my changes thoroughly
  • For provider changes: Re-recorded VCR cassettes with bundle exec rake vcr:record[provider_name] N/A
  • All tests pass: bundle exec rspec
• I updated documentation if needed N/A
• I didn't modify auto-generated files manually (models.json, aliases.json)

AI-generated code

• I used AI tools to help write this code
• I have reviewed and understand all generated code (required if above is checked)

API changes

• Breaking change
• New public methods/classes
• Changed method signatures
• No API changes

[jayelkaake]

@crmne thanks for the quick review!

[crmne]

@crmne thanks for the quick review!

Bug fixes like these are very important. Thanks for the PR!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.41%. Comparing base (0b39814) to head (4005e07).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #668   +/-   ##
=======================================
  Coverage   81.41%   81.41%           
=======================================
  Files         116      116           
  Lines        5489     5489           
  Branches     1433     1433           
=======================================
  Hits         4469     4469           
  Misses       1020     1020           

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