Specify runtime versions to install

Author: pranavkm

build/repo.props

@@ -1,12 +1,18 @@
 <Project>
+  <Import Project="dependencies.props" />
+
   <ItemGroup>
     <ExcludeFromTest Include="$(RepositoryRoot)test\Microsoft.AspNetCore.Hosting.TestSites\Microsoft.AspNetCore.Hosting.TestSites.csproj" />
     <ExcludeFromTest Include="$(RepositoryRoot)test\TestStartupAssembly1\TestStartupAssembly1.csproj" />
   </ItemGroup>
-
   <PropertyGroup>
     <!-- These properties are use by the automation that updates dependencies.props -->
     <LineupPackageId>Internal.AspNetCore.Universe.Lineup</LineupPackageId>
     <LineupPackageRestoreSource>https://dotnet.myget.org/F/aspnetcore-dev/api/v3/index.json</LineupPackageRestoreSource>
   </PropertyGroup>
+
+  <ItemGroup>
+    <DotNetCoreRuntime Include="$(MicrosoftNETCoreApp20PackageVersion)" />
+    <DotNetCoreRuntime Include="$(MicrosoftNETCoreApp21PackageVersion)" />
+  </ItemGroup>
 </Project>