Bump Google.Protobuf in /src/Tests/Coding.Blog.UnitTests (#313)

Bumps [Google.Protobuf](https://github.com/protocolbuffers/protobuf) from 3.21.5 to 3.21.6.
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Changelog](https://github.com/protocolbuffers/protobuf/blob/main/generate_changelog.py)
- [Commits](protocolbuffers/protobuf@v3.21.5...v3.21.6)

---
updated-dependencies:
- dependency-name: Google.Protobuf
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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src/Coding.Blog/Engine/Coding.Blog.Engine.csproj

@@ -9,7 +9,7 @@
 	<ItemGroup>
 		<PackageReference Include="Autofac.Extensions.DependencyInjection" Version="8.0.0" />
 		<PackageReference Include="Flurl.Http" Version="3.2.4" />
-		<PackageReference Include="Google.Protobuf" Version="3.21.5" />
+		<PackageReference Include="Google.Protobuf" Version="3.21.6" />
 		<PackageReference Include="Grpc.Net.Client" Version="2.48.0" />
 		<PackageReference Include="Grpc.Tools" Version="2.48.1">
 			<PrivateAssets>all</PrivateAssets>