chore(deps): bump the nuget group in /build with 1 update (#2310)

Bumps the nuget group in /build with 1 update: [NuGet.Protocol](https://github.com/NuGet/NuGet.Client).


Updates `NuGet.Protocol` from 6.6.1 to 6.9.1
- [Release notes](https://github.com/NuGet/NuGet.Client/releases)
- [Commits](https://github.com/NuGet/NuGet.Client/commits)

---
updated-dependencies:
- dependency-name: NuGet.Protocol
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: nuget
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

build/NugetValidator/NugetValidator.csproj

@@ -14,7 +14,7 @@
 
   <ItemGroup>
     <PackageReference Include="CommandLineParser" Version="2.9.1" />
-    <PackageReference Include="NuGet.Protocol" Version="6.6.1" />
+    <PackageReference Include="NuGet.Protocol" Version="6.9.1" />
     <PackageReference Include="YamlDotNet" Version="15.1.2" />
   </ItemGroup>