Fix running microbenchmarks on .NET 6 (#1579)

Author: JamesNK

build/dependencies.props

@@ -1,6 +1,6 @@
 <Project>
   <PropertyGroup>
-    <BenchmarkDotNetPackageVersion>0.12.1</BenchmarkDotNetPackageVersion>
+    <BenchmarkDotNetPackageVersion>0.13.1</BenchmarkDotNetPackageVersion>
     <GoogleProtobufPackageVersion>3.18.1</GoogleProtobufPackageVersion>
     <GrpcDotNetPackageVersion>2.42.0-pre1</GrpcDotNetPackageVersion>  <!-- Used by example projects -->
     <GrpcPackageVersion>2.43.0</GrpcPackageVersion>

perf/Grpc.AspNetCore.Microbenchmarks/DefaultCoreConfig.cs

@@ -43,7 +43,7 @@ public DefaultCoreConfig()
             AddValidator(JitOptimizationsValidator.FailOnError);
 
             AddJob(Job.Default
-                .WithToolchain(CsProjCoreToolchain.From(new NetCoreAppSettings("netcoreapp3.1", null, ".NET Core 3.1")))
+                .WithToolchain(CsProjCoreToolchain.From(new NetCoreAppSettings("net6.0", null, ".NET 6")))
                 .WithGcMode(new GcMode { Server = true })
                 .WithStrategy(RunStrategy.Throughput));
         }