[tests] Add CoreCLR test variation. (#24209)

Author: rolfbjarne

tests/common/test-variations.csproj

@@ -8,6 +8,7 @@
 		<TestVariations Include="nativeaot" Description="Run with NativeAOT ('PublishAot=true' and '_IsPublishing=true')" />
 		<TestVariations Include="linksdk" Description="Run with trimmer (MtouchLink/LinkMode) set to 'SdkOnly'" />
 		<TestVariations Include="linkall" Description="Run with trimmer (MtouchLink/LinkMode) set to 'Full'" />
+		<TestVariations Include="coreclr" Description="Use CoreCLR ('UseMonoRuntime=false')" />
 	</ItemGroup>
 
 	<PropertyGroup Condition="'$(TestVariation)' == 'interpreter'">
@@ -42,6 +43,10 @@
 		<_IsPublishing>true</_IsPublishing>
 	</PropertyGroup>
 
+	<PropertyGroup Condition="'$(TestVariation)' == 'coreclr'">
+		<UseMonoRuntime>false</UseMonoRuntime>
+	</PropertyGroup>
+
 	<Target Name="ValidateTestVariation" Condition="'$(TestVariation)' != '' And '$(OutputType)' == 'exe'" BeforeTargets="Build">
 		<ItemGroup>
 			<_FilteredTestVariations Include="@(TestVariations)" Condition="'%(Identity)' == '$(TestVariation)'" />