Fix client factory trim warning

[JamesNK]

Fix warning:

/_/src/Grpc.Net.ClientFactory/Internal/DefaultClientActivator.cs(27,85): Trim analysis warning IL2087: Grpc.Net.ClientFactory.Internal.DefaultClientActivator<TClien
t>.<>c.<.cctor>b__9_0(): 'instanceType' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicConstructors' in call to 'Microsoft.Extensions.DependencyInj
ection.ActivatorUtilities.CreateFactory(Type, Type[])'. The generic parameter 'TClient' of 'Grpc.Net.ClientFactory.Internal.DefaultClientActivator<TClient>.<>c' doe
s not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to. [C:\Develo
pment\Source\grpc-dotnet\examples\Aggregator\Server\Server.csproj]