test(openai-agents): Replace mocks with httpx in MCP tool tests

[alexander-alderman-webb]

Description

Replace mocks with httpx types to avoid test failures when library internals change.

Issues

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

[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

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Bug Fixes 🐛

• (celery) Propagate user-set headers by sentrivana in #5581
• (utils) Avoid double serialization of strings in safe_serialize by ericapisani in #5587

Documentation 📚

• (openai-agents) Remove inapplicable comment by alexander-alderman-webb in #5495
• Add AGENTS.md by sentrivana in #5579
• Add set_attribute example to changelog by sentrivana in #5578

Internal Changes 🔧

Openai Agents

• Replace mocks with httpx in MCP tool tests by alexander-alderman-webb in #5605

• Expect namespace tool field for new openai versions by alexander-alderman-webb in #5599

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_{🤖 This preview updates automatically when you update the PR.}

[github-actions]

Codecov Results 📊

✅ 52 passed | Total: 52 | Pass Rate: 100% | Execution Time: 6.70s

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	—
Failed Tests	—
Skipped Tests	—

✨ No test changes detected

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 14816 uncovered lines.
❌ Project coverage is 25.64%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
- Coverage    25.65%    25.64%    -0.01%
==========================================
  Files          189       189         —
  Lines        19924     19924         —
  Branches      6458      6458         —
==========================================
+ Hits          5111      5108        -3
- Misses       14813     14816        +3
- Partials       431       430        -1

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