Update protobuf requirement in /src/bindings/python

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](https://github.com/protocolbuffers/protobuf/compare/v3.18.1...v5.26.0)

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

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

src/bindings/python/constraints.txt

@@ -20,5 +20,5 @@ docopt~=0.6.2
 paddlepaddle==2.5.2
 tensorflow>=1.15.5,<2.16.0
 six~=1.16.0
-protobuf>=3.18.1,<4.0.0
+protobuf>=3.18.1,<6.0.0
 onnx==1.15.0