Bump litellm[proxy] from 1.52.9 to 1.52.15

Bumps [litellm[proxy]](https://github.com/BerriAI/litellm) from 1.52.9 to 1.52.15.
- [Release notes](https://github.com/BerriAI/litellm/releases)
- [Commits](BerriAI/litellm@v1.52.9...v1.52.15)

---
updated-dependencies:
- dependency-name: litellm[proxy]
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -1,3 +1,3 @@
 google-cloud-aiplatform==1.73.0
 anthropic[vertex]==0.39.0
-litellm[proxy]==1.52.9
+litellm[proxy]==1.52.15