Bump gradio from 6.0.2 to 6.7.0 in /backend-agent

Bumps [gradio](https://github.com/gradio-app/gradio) from 6.0.2 to 6.7.0.
- [Release notes](https://github.com/gradio-app/gradio/releases)
- [Changelog](https://github.com/gradio-app/gradio/blob/main/CHANGELOG.md)
- [Commits](https://github.com/gradio-app/gradio/compare/gradio@6.0.2...gradio@6.7.0)

---
updated-dependencies:
- dependency-name: gradio
  dependency-version: 6.7.0
  dependency-type: indirect
...

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

Author: dependabot[bot]