Update to .NET Core 3 preview 9 (#380)

Author: AlekseyMartynov

appveyor.yml

@@ -9,7 +9,7 @@ install:
   # TODO remove when .NET Core 3.0 stable is available
   - nuget update -self
   - ps: "Invoke-WebRequest -Uri https://dot.net/v1/dotnet-install.ps1 -UseBasicParsing -OutFile $env:temp\\dotnet-install.ps1"
-  - ps: "& $env:temp\\dotnet-install.ps1 -Architecture x64 -Version 3.0.100-preview7-012821 -InstallDir $env:ProgramFiles\\dotnet"
+  - ps: "& $env:temp\\dotnet-install.ps1 -Architecture x64 -Version 3.0.100-preview9-014004 -InstallDir $env:ProgramFiles\\dotnet"
 
   - if defined RELEASE_KEY_SECRET (nuget install secure-file -ExcludeVersion -Verbosity quiet && secure-file\tools\secure-file -decrypt net\DevExtreme.AspNet.Data\release.snk.enc -secret %RELEASE_KEY_SECRET%)
   - nuget install -Verbosity quiet -ExcludeVersion -OutputDirectory . OpenCover

net/DevExtreme.AspNet.Data.Tests.EFCore/RemoteGroupingStress.cs

@@ -17,11 +17,7 @@ public class DataItem : RemoteGroupingStressHelper.IEntity {
             public DateTime? NullDate { get; set; }
         }
 
-        [Fact(
-#if EFCORE3
-            Skip = "https://github.com/aspnet/EntityFrameworkCore/issues/16844"
-#endif
-        )]
+        [Fact]
         public async Task Scenario() {
             await TestDbContext.ExecAsync(context => {
                 var dbSet = context.Set<DataItem>();

net/DevExtreme.AspNet.Data.Tests.EFCore3/DevExtreme.AspNet.Data.Tests.EFCore3.csproj

@@ -6,7 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.0.0-preview8.19405.11" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.0.0-preview9.19423.6" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.7.0" />
     <PackageReference Include="xunit" Version="2.3.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.3.1" />