ci: Remove tomli from requirements-testing.txt

[alexander-alderman-webb]

Description

tomli is already declared as a dependency of pytest:

https://github.com/pytest-dev/pytest/blob/2eac0d6cfe0be3d2d49b86c3860ee00f60517813/pyproject.toml#L56

Remove the package from requirements-testing.txt and add the package as a dependency to only the test suites that rely on the package (if applicable).

This is part of environment cleanup before moving the remaining testing dependencies to a uv dependency group.

Issues

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 📊

✅ 91388 passed | ⏭️ 6136 skipped | Total: 97524 | Pass Rate: 93.71% | Execution Time: 329m 8s

📊 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 2406 uncovered lines.
✅ Project coverage is 89.87%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.84%    89.87%    +0.03%
==========================================
  Files          192       192         —
  Lines        23758     23758         —
  Branches      8204      8204         —
==========================================
+ Hits         21346     21352        +6
- Misses        2412      2406        -6
- Partials      1345      1347        +2

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