chore(deps-dev): bump llama-index

Bumps [llama-index](https://github.com/run-llama/llama_index) from 0.12.8 to 0.12.28.
- [Release notes](https://github.com/run-llama/llama_index/releases)
- [Changelog](https://github.com/run-llama/llama_index/blob/main/CHANGELOG.md)
- [Commits](run-llama/llama_index@v0.12.8...v0.12.28)

---
updated-dependencies:
- dependency-name: llama-index
  dependency-version: 0.12.28
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]