fix(litellm): Avoid double span exits when streaming

[alexander-alderman-webb]

Description

Only exit the span on the final invocation of _success_callback when litellm streams a response.

The litellm.success_callback callbacks are fired multiple times when streaming a response with litellm.

Avoid an unhandled SDK exception by using litellm like a user would in the relevant test.

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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New Features ✨

• (integrations) Instrument pyreqwest tracing by servusdei2018 in #5682

Bug Fixes 🐛

• (litellm) Avoid double span exits when streaming by alexander-alderman-webb in #5933

Internal Changes 🔧

• (opentelemetry) Ignore mypy error by alexander-alderman-webb in #5927
• Update validate-pr workflow by stephanie-anderson in #5931

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

[github-actions]

Codecov Results 📊

✅ 13 passed | Total: 13 | Pass Rate: 100% | Execution Time: 8.81s

All tests are passing successfully.

❌ Patch coverage is 0.00%. Project has 14771 uncovered lines.

Files with missing lines (1)

File	Patch %	Lines
litellm.py	0.00%	⚠️ 140 Missing

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