test(httpx): Replace deprecated asyncio.iscoroutinefunction

[alexander-alderman-webb]

Description

For the purpose of the test, inspect.iscoroutinefunction is equivalent to asyncio.iscoroutinefunction.

Issues

Contributes to #4900

Reminders

• Please add tests to validate your changes, and lint your code using uv run ruff.
• 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]

Codecov Results 📊

✅ 94982 passed | ⏭️ 6343 skipped | Total: 101325 | Pass Rate: 93.74% | Execution Time: 339m 11s

📊 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 2511 uncovered lines.
✅ Project coverage is 89.89%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.88%    89.89%    +0.01%
==========================================
  Files          193       193         —
  Lines        24834     24834         —
  Branches      8912      8912         —
==========================================
+ Hits         22321     22323        +2
- Misses        2513      2511        -2
- Partials      1417      1415        -2

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