Bump litellm from 1.81.3 to 1.81.6

Bumps [litellm](https://github.com/BerriAI/litellm) from 1.81.3 to 1.81.6.
- [Release notes](https://github.com/BerriAI/litellm/releases)
- [Commits](https://github.com/BerriAI/litellm/commits)

---
updated-dependencies:
- dependency-name: litellm
  dependency-version: 1.81.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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Author: dependabot[bot]