Fix build failure on benchmark server V2

[JamesNK]

Fix new error:

C:\Users\Administrator\AppData\Local\Temp\benchmarks-agent\benchmarks-server-7736\j3wrywbc.imh\grpc-dotnet\src\Grpc.AspNetCore.Server\Internal\HttpContextStreamWriter.cs(54,40): error CS0539: 'HttpContextStreamWriter.WriteAsync(TResponse, CancellationToken)' in explicit interface declaration is not found among members of the interface that can be implemented [C:\Users\Administrator\AppData\Local\Temp\benchmarks-agent\benchmarks-server-7736\j3wrywbc.imh\grpc-dotnet\src\Grpc.AspNetCore.Server\Grpc.AspNetCore.Server.csproj::TargetFramework=net7.0]