fix: bump gradio from 6.15.0 to 6.15.1 in /packages/bigframes

Bumps [gradio](https://github.com/gradio-app/gradio) from 6.15.0 to 6.15.1.
- [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@6.15.0...gradio@6.15.1)

---
updated-dependencies:
- dependency-name: gradio
  dependency-version: 6.15.1
  dependency-type: direct:production
...

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

Author: dependabot[bot]

packages/bigframes/testing/constraints-3.11.txt

@@ -172,7 +172,7 @@ google-pasta==0.2.0
 google-resumable-media==2.7.2
 googleapis-common-protos==1.70.0
 googledrivedownloader==1.1.0
-gradio==6.15.0
+gradio==6.15.1
 gradio_client==1.11.0
 graphviz==0.21
 greenlet==3.2.3