Fix MessagePack vulnerability GHSA-hv8m-jj95-wg3x by pinning to 2.5.301

Author: Copilot

dotnet/Directory.Packages.props

@@ -13,6 +13,7 @@
     <PackageVersion Include="CommunityToolkit.Aspire.Hosting.Dapr" Version="9.9.0" />
     <PackageVersion Include="CommunityToolkit.Aspire.Hosting.NodeJS.Extensions" Version="9.9.0" />
     <PackageVersion Include="Aspire.Hosting.Azure.Search" Version="13.0.0" />
+    <PackageVersion Include="MessagePack" Version="2.5.301" /><!-- Vulnerability fix: GHSA-hv8m-jj95-wg3x; transitively pinned via Aspire.Hosting.AppHost -->
     <PackageVersion Include="AWSSDK.BedrockAgent" Version="4.0.7.5" />
     <PackageVersion Include="AWSSDK.BedrockAgentRuntime" Version="4.0.8.5" />
     <PackageVersion Include="AWSSDK.BedrockRuntime" Version="4.0.14.5" />

dotnet/samples/Demos/AgentFrameworkWithAspire/ChatWithAgent.AppHost/ChatWithAgent.AppHost.csproj

@@ -20,6 +20,7 @@
 
   <ItemGroup>
     <PackageReference Include="Aspire.Hosting.AppHost" />
+    <PackageReference Include="MessagePack" /><!-- Pin to patched version; overrides vulnerable transitive 2.5.192 from Aspire.Hosting.AppHost (GHSA-hv8m-jj95-wg3x) -->
     <PackageReference Include="Aspire.Hosting.Azure.CognitiveServices" />
     <PackageReference Include="Aspire.Hosting.Azure.Search" />
   </ItemGroup>