Bump third_party/pigweed/repo from cbbc73d to 9640cde (#31414)

Bumps [third_party/pigweed/repo](https://github.com/google/pigweed) from `cbbc73d` to `9640cde`.
- [Commits](google/pigweed@cbbc73d...9640cde)

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

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