test: Add span origin span streaming tests

[sentrivana]

Description

Span origin is just a regular attribute in span streaming, so it might not actually need separate tests. However, the case where we check that it's set to manual by default makes sense to cover, so added streaming counterparts to the two existing origin tests.

Issues

Part of #5395

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 📊

✅ 89952 passed | ⏭️ 6288 skipped | Total: 96240 | Pass Rate: 93.47% | Execution Time: 312m 44s

📊 Comparison with Base Branch

Metric	Change
Total Tests	📈 +30
Passed Tests	📈 +30
Failed Tests	—
Skipped Tests	—

All tests are passing successfully.

✅ Patch coverage is 100.00%. Project has 2435 uncovered lines.
✅ Project coverage is 89.77%. Comparing base (base) to head (head).

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    89.77%    89.77%        —%
==========================================
  Files          192       192         —
  Lines        23809     23809         —
  Branches      8218      8218         —
==========================================
+ Hits         21374     21374         —
- Misses        2435      2435         —
- Partials      1347      1347         —

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