Update protobuf requirement from <3.21 to <5.30

Updates the requirements on [protobuf](https://github.com/protocolbuffers/protobuf) to permit the latest version.
- [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...v5.29.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

setup.py

@@ -23,7 +23,7 @@ def readme():
         "larq>=0.9.2,<0.13.2",
         "zookeeper>=1.0.0",
         "typeguard<3.0.0",
-        "protobuf<3.21",
+        "protobuf<5.30",
         "importlib-metadata ~= 2.0 ; python_version<'3.8'",
     ],
     extras_require={