Add explicit dependency to types-protobuf

This is for running `mypy`. For some unknown reason before migrating to
repo-config this dependency was pulled automatically (probably by the
`--install-types` `mypy` option) but now it isn't anymore.

Without this, `mypy` crashes with this error:

```
nox > mypy --install-types --namespace-packages --non-interactive --explicit-package-bases --strict -p frequenz.sdk -p benchmarks -p docs -p examples -p noxfile -p tests -p src
Traceback (most recent call last):
  File "/home/luca/devel/sdk/.nox/mypy/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
             ^^^^^^^^^^^^^^^
  File "/home/luca/devel/sdk/.nox/mypy/lib/python3.11/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
  File "mypy/main.py", line 95, in main
  File "mypy/main.py", line 174, in run_build
  File "mypy/build.py", line 197, in build
  File "mypy/build.py", line 270, in _build
  File "mypy/build.py", line 2927, in dispatch
  File "mypy/build.py", line 3325, in process_graph
  File "mypy/build.py", line 3441, in process_stale_scc
  File "mypy/build.py", line 2586, in generate_unused_ignore_notes
  File "mypy/errors.py", line 672, in generate_unused_ignore_errors
  File "mypy/errors.py", line 439, in _add_error_info
AssertionError
```

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

pyproject.toml

@@ -67,7 +67,8 @@ dev-mkdocs = [
 ]
 dev-mypy = [
   "mypy == 1.4.1",
-  "grpc-stubs == 1.24.12", # This dependency introduces breaking changes in patch releases
+  "grpc-stubs == 1.24.12",      # This dependency introduces breaking changes in patch releases
+  "types-protobuf == 4.23.0.1",
   # For checking the noxfile, docs/ script, and tests
   "frequenz-sdk[dev-mkdocs,dev-noxfile,dev-pytest]",
 ]