test(openai-agents): Remove MagicMock from ModelResponse

[alexander-alderman-webb]

Description

Remove the function property from tool calls in mocked model responses.

The commit openai/openai-agents-python@a776d80 broke our test suite because instances of ResponseFunctionToolCall are now serialized inside openai-agents. As we attach a non-serializable MagicMock to the instances, our test suite faces an unhandled exception starting with openai-agents version 0.6.0.

The model ResponseFunctionToolCall does not declare a function field: openai/openai-python@main/src/openai/types/responses/response_function_tool_call.py

Issues

Closes #5124

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.98%. Comparing base (c63e8d8) to head (0d6e72b).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5126      +/-   ##
==========================================
- Coverage   84.01%   83.98%   -0.03%     
==========================================
  Files         180      180              
  Lines       18168    18168              
  Branches     3227     3227              
==========================================
- Hits        15263    15259       -4     
- Misses       1916     1921       +5     
+ Partials      989      988       -1     

see 2 files with indirect coverage changes