chore(deps): Bump System.Security.Cryptography.Xml for CVEs (#1449)

Pins System.Security.Cryptography.Xml to 9.0.18 to remediate CVE-2026-26171 and CVE-2026-33116 in the Typewriter project.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot-Session: b925a358-5d34-4537-8327-fe1fa580d903

Author: gavinbarron

src/Typewriter/Typewriter.csproj

@@ -22,6 +22,7 @@
     <PackageReference Include="Microsoft.Extensions.Configuration.EnvironmentVariables" Version="9.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="9.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Xml" Version="9.0.3" />
+    <PackageReference Include="System.Security.Cryptography.Xml" Version="9.0.18" />
     <PackageReference Include="Nito.AsyncEx">
       <Version>5.1.2</Version>
     </PackageReference>