Fix System.Security.Cryptography.Xml vulnerabilities

Bump System.Security.Cryptography.Xml from 10.0.5 to 10.0.6 to address CVE-2026-33116 and CVE-2026-26171.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: b925a358-5d34-4537-8327-fe1fa580d903

Author: gavinbarron

src/Microsoft.OpenApi.Workbench/Microsoft.OpenApi.Workbench.csproj

@@ -26,6 +26,7 @@
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
     <PackageReference Include="Microsoft.Windows.Compatibility" Version="10.0.5" />
+    <PackageReference Include="System.Security.Cryptography.Xml" Version="10.0.6" />
   </ItemGroup>
 
   <!-- Windows-specific resources -->