Bump third_party/nanopb/repo from 5fd8f04 to cf26d28 (#31281)

Bumps [third_party/nanopb/repo](https://github.com/nanopb/nanopb) from `5fd8f04` to `cf26d28`.
- [Commits](nanopb/nanopb@5fd8f04...cf26d28)

---
updated-dependencies:
- dependency-name: third_party/nanopb/repo
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>