Bump third_party/nanopb/repo from `a4bbd6a` to `9766c45` (#29902)

Bumps [third_party/nanopb/repo](https://github.com/nanopb/nanopb) from `a4bbd6a` to `9766c45`.
- [Commits](https://github.com/nanopb/nanopb/compare/a4bbd6a2ebff89d4e723e396ce27eef433a4f23c...9766c4589f61b76807a0a394040c15a2d23ef24c)

---
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>
diff --git a/third_party/nanopb/repo b/third_party/nanopb/repo
index a4bbd6a..9766c45 160000
--- a/third_party/nanopb/repo
+++ b/third_party/nanopb/repo
@@ -1 +1 @@
-Subproject commit a4bbd6a2ebff89d4e723e396ce27eef433a4f23c
+Subproject commit 9766c4589f61b76807a0a394040c15a2d23ef24c