Update protobuf requirement from <7,>=6.31.1 to >=6.31.1,<8 (#254)

Updates the requirements on
[protobuf](https://github.com/protocolbuffers/protobuf) to permit the
latest version.
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Author: frequenz-auto-dependabot[bot]

pyproject.toml

@@ -43,7 +43,7 @@ dependencies = [
   "frequenz-client-common >= 0.3.6, < 0.4.0",
   "frequenz-core >= 1.3.0, < 2.0.0",
   "grpcio >= 1.72.1, < 2",
-  "protobuf >= 6.31.1, < 7",
+  "protobuf >= 6.31.1, < 8",
   "typing-extensions >= 4.13.0, < 5",
 ]
 dynamic = ["version"]