Update protobuf requirement in the pip group across 1 directory

Updates the requirements on [protobuf](https://github.com/protocolbuffers/protobuf) to permit the latest version.

Updates `protobuf` to 5.28.0
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/protobuf_release.bzl)
- [Commits](protocolbuffers/protobuf@v2.4.1...v5.28.0)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-type: direct:production
  dependency-group: pip
...

Signed-off-by: dependabot[bot] <support@github.com>

pyproject.toml

@@ -8,7 +8,7 @@ authors = [
 dependencies = [
  "fava>=1.26",
  "beangrow>=1.0.0",
- "protobuf<3.21",
+ "protobuf<5.29",
 ]
 readme = "README.md"
 requires-python = ">= 3.8"