Reduce noise in the logs while disposing RpcInitializationService

Following is an unhandled exception:

```
System.AggregateException: One or more errors occurred. (One or more errors occurred. (Operation is not valid due to the current state of the object.)) ---> System.AggregateException: One or more errors occurred. (Operation is not valid due to the current state of the object.) ---> System.InvalidOperationException: Operation is not valid due to the current state of the object.
at Grpc.Core.Utils.GrpcPreconditions.CheckState(Boolean condition)
at Grpc.Core.Server.ShutdownInternalAsync(Boolean kill)
at Microsoft.Azure.WebJobs.Script.Workers.Rpc.RpcInitializationService.OuterStopAsync(CancellationToken cancellationToken) in /src/azure-functions-host/src/WebJobs.Script/Workers/Rpc/RpcInitializationService.cs:line 108
at Microsoft.Azure.WebJobs.Script.HostedServiceManager.StopAsync(CancellationToken cancellationToken) in /src/azure-functions-host/src/WebJobs.Script/HostedServiceManager.cs:line 27
at Microsoft.AspNetCore.Hosting.HostedServiceExecutor.ExecuteAsync(Func`2 callback, Boolean throwOnFirstFailure)
--- End of inner exception stack trace ---
at Microsoft.AspNetCore.Hosting.HostedServiceExecutor.ExecuteAsync(Func`2 callback, Boolean throwOnFirstFailure)
at Microsoft.AspNetCore.Hosting.WebHost.StopAsync(CancellationToken cancellationToken)
at Microsoft.AspNetCore.Hosting.WebHostExtensions.WaitForTokenShutdownAsync(IWebHost host, CancellationToken token)
at Microsoft.AspNetCore.Hosting.WebHostExtensions.RunAsync(IWebHost host, CancellationToken token, String startupMessage)
at Microsoft.AspNetCore.Hosting.WebHostExtensions.RunAsync(IWebHost host, CancellationToken token, String startupMessage)
at Microsoft.AspNetCore.Hosting.WebHostExtensions.RunAsync(IWebHost host, CancellationToken token)
--- End of inner exception stack trace ---
at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
at System.Threading.Tasks.Task.Wait()
at Microsoft.Azure.WebJobs.Script.WebHost.Program.Main(String[] args) in /src/azure-functions-host/src/WebJobs.Script.WebHost/Program.cs:line 31
```

Needs investigation