Bump dspy-ai from 2.5.7 to 2.5.28

Bumps [dspy-ai](https://github.com/stanfordnlp/dsp) from 2.5.7 to 2.5.28.
- [Release notes](https://github.com/stanfordnlp/dsp/releases)
- [Commits](stanfordnlp/dspy@2.5.7...2.5.28)

---
updated-dependencies:
- dependency-name: dspy-ai
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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