chore(deps): bump the langchain group across 1 directory with 2 updates (#1014)

Bumps the langchain group with 2 updates in the / directory: [langchain](https://github.com/langchain-ai/langchain) and [langchain-google-vertexai](https://github.com/langchain-ai/langchain-google).


Updates `langchain` from 0.3.8 to 0.3.9
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==0.3.8...langchain==0.3.9)

Updates `langchain-google-vertexai` from 2.0.3 to 2.0.8
- [Release notes](https://github.com/langchain-ai/langchain-google/releases)
- [Commits](langchain-ai/langchain-google@libs/genai/v2.0.3...libs/vertexai/v2.0.8)

---
updated-dependencies:
- dependency-name: langchain
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: langchain
- dependency-name: langchain-google-vertexai
  dependency-type: direct:development
  update-type: version-update:semver-patch
  dependency-group: langchain
...

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Author: dependabot[bot]