chore(deps): Bump braintrust from 3.18.0 to 3.20.0 in /eval

Bumps [braintrust](https://github.com/braintrustdata/braintrust-sdk-javascript/tree/HEAD/js) from 3.18.0 to 3.20.0.
- [Release notes](https://github.com/braintrustdata/braintrust-sdk-javascript/releases)
- [Changelog](https://github.com/braintrustdata/braintrust-sdk-javascript/blob/main/js/CHANGELOG.md)
- [Commits](https://github.com/braintrustdata/braintrust-sdk-javascript/commits/braintrust@3.20.0/js)

---
updated-dependencies:
- dependency-name: braintrust
  dependency-version: 3.20.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

eval/package-lock.json

@@ -39,7 +39,7 @@
     "@actions/github": "^9.1.1",
     "@braintrust/core": "^0.0.95",
     "axios": "^1.7.9",
-    "braintrust": "^3.18.0",
+    "braintrust": "^3.20.0",
     "zod": "^3.23.4"
   },
   "devDependencies": {