Bump third_party/nanopb/repo from 671672b to fc7d53c

Bumps [third_party/nanopb/repo](https://github.com/nanopb/nanopb) from `671672b` to `fc7d53c`.
- [Commits](nanopb/nanopb@671672b...fc7d53c)

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

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