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
...

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