Suppress TimeProvider.Testing net472 warning

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

tests/ModelContextProtocol.Tests/ModelContextProtocol.Tests.csproj

@@ -21,6 +21,11 @@
     <JsonSerializerIsReflectionEnabledByDefault>false</JsonSerializerIsReflectionEnabledByDefault>
   </PropertyGroup>
 
+  <PropertyGroup Condition="'$(TargetFramework)' == 'net472'">
+    <!-- Suppress warning that Microsoft.Extensions.TimeProvider.Testing hasn't been tested with net472 -->
+    <SuppressTfmSupportBuildWarnings>true</SuppressTfmSupportBuildWarnings>
+  </PropertyGroup>
+
   <PropertyGroup>
     <!-- Without this, tests are currently not showing results until all tests complete
          https://xunit.net/docs/getting-started/v3/microsoft-testing-platform