test: Update AspNetCoreMvcCoreFrameworkApplication to ASP.NET Core 2.3 (#3525)

Update AspNetCoreMvcCoreFrameworkApplication to ASP.NET Core 2.3

Author: nr-ahemsath

tests/Agent/IntegrationTests/Applications/AspNetCoreMvcCoreFrameworkApplication/AspNetCoreMvcCoreFrameworkApplication.csproj

@@ -9,8 +9,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.AspNetCore" Version="2.1.7" />
-    <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="2.1.3" />
+    <PackageReference Include="Microsoft.AspNetCore" Version="2.3.9" />
+    <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="2.3.9" />
     <PackageReference Include="Microsoft.VisualStudio.Threading.Analyzers" Version="17.14.15">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>

tests/Agent/IntegrationTests/Applications/AspNetCoreMvcCoreFrameworkApplication/Startup.cs

@@ -25,6 +25,10 @@ public void ConfigureServices(IServiceCollection services)
         services
             .AddMvcCore()
             .AddJsonFormatters()
+            // Despite this application now using a 2.3 version of ASP.NET Core,
+            // 2.1 is still an appropriate compatibility version to use for this application,
+            // since 2.3 is just a reshipping of 2.1.  See Microsoft's announcement of
+            // ASP.NET Core 2.3 for more details: https://github.com/dotnet/announcements/issues/331
             .SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
     }
 
@@ -38,4 +42,4 @@ public void Configure(IApplicationBuilder app, IHostingEnvironment env)
 
         app.UseMvc();
     }
-}
+}