Bump protobuf from 4.21.6 to 4.25.8

Bumps [protobuf](https://github.com/protocolbuffers/protobuf) from 4.21.6 to 4.25.8.
- [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/commits/v4.25.8)

---
updated-dependencies:
- dependency-name: protobuf
  dependency-version: 4.25.8
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -8,7 +8,7 @@ scipy
 # with both new and old protobuf stubs. This is needed to resolve
 # Keras-TensorFlow circular dependency issue, when one of them gets a dependency
 # incompatible with another one (protobuf in this specific case).
-protobuf==4.21.6
+protobuf==4.25.8
 tf-nightly
 portpicker
 pyyaml