Bump third_party/pigweed/repo from e61718e to 834e876 (#19220)

Bumps [third_party/pigweed/repo](https://github.com/google/pigweed) from `e61718e` to `834e876`.
- [Release notes](https://github.com/google/pigweed/releases)
- [Commits](google/pigweed@e61718e...834e876)

---
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>