Bump NuGet.Packaging and NuGet.Protocol (#1007)

Updated [NuGet.Packaging](https://github.com/NuGet/NuGet.Client) from
6.12.5 to 7.3.1.

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<summary>Release notes</summary>

_Sourced from [NuGet.Packaging's
releases](https://github.com/NuGet/NuGet.Client/releases)._

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Commits viewable in [compare
view](https://github.com/NuGet/NuGet.Client/commits).
</details>

Updated [NuGet.Protocol](https://github.com/NuGet/NuGet.Client) from
6.12.5 to 7.3.1.

<details>
<summary>Release notes</summary>

_Sourced from [NuGet.Protocol's
releases](https://github.com/NuGet/NuGet.Client/releases)._

No release notes found for this version range.

Commits viewable in [compare
view](https://github.com/NuGet/NuGet.Client/commits).
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Directory.Packages.props

@@ -45,8 +45,8 @@
     <PackageVersion Include="Microsoft.SemanticKernel.Connectors.PgVector" Version="$(SemanticKernelVersion)-preview" />
     <PackageVersion Include="Microsoft.SourceLink.GitHub" Version="10.0.202" />
     <!-- Pin to patched versions; NuGet.Protocol 6.12.5+ fixes GHSA-g4vj-cjjj-v7hg (pulled in by Microsoft.VisualStudio.Web.CodeGeneration.Design) -->
-    <PackageVersion Include="NuGet.Packaging" Version="6.12.5" />
-    <PackageVersion Include="NuGet.Protocol" Version="6.12.5" />
+    <PackageVersion Include="NuGet.Packaging" Version="7.3.1" />
+    <PackageVersion Include="NuGet.Protocol" Version="7.3.1" />
     <PackageVersion Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" Version="1.23.0" />
     <PackageVersion Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="10.0.2" />
     <PackageVersion Include="Microsoft.Extensions.AI.OpenAI" Version="10.0.1-preview.1.25571.5" />