Don't mark unannotated test project as trimmable

Author: sbomer

src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/Microsoft.Extensions.DependencyInjection.Specification.Tests.csproj

@@ -7,6 +7,7 @@
     <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>
     <CLSCompliant>false</CLSCompliant>
     <IsPackable>true</IsPackable>
+    <IsTrimmable>false</IsTrimmable>
     <PackageDescription>Suite of xUnit.net tests to check for container compatibility with Microsoft.Extensions.DependencyInjection.</PackageDescription>
     <!-- this assembly doesn't need to be binplaced -->
     <EnableBinPlacing>false</EnableBinPlacing>