Fix wrong path after the TFM change (dotnet/linker#2204)

Commit migrated from dotnet/linker@272bd6d

Author: vitek-karas

src/tools/illink/src/ILLink.Tasks/ILLink.Tasks.csproj

@@ -2,6 +2,7 @@
   <PropertyGroup>
     <!-- Keep these in sync with ILLinkTasksAssembly in Microsoft.NET.ILLInk.Tasks.props. -->
     <!-- Keep the net#.0 TFM in sync with the Mono.Linker.csproj condition below. -->
+    <!-- Keep the net#.0 TFM in sync with the code in LinkTask.cs in method ILLink.ILLinkPath. -->
     <TargetFrameworks>net6.0;net472</TargetFrameworks>
     <EnableDefaultCompileItems>false</EnableDefaultCompileItems>
     <Description>MSBuild tasks for running the IL Linker</Description>

src/tools/illink/src/ILLink.Tasks/LinkTask.cs

@@ -253,7 +253,7 @@ public string ILLinkPath {
 
 				var taskDirectory = Path.GetDirectoryName (Assembly.GetExecutingAssembly ().Location);
 				// The linker always runs on .NET Core, even when using desktop MSBuild to host ILLink.Tasks.
-				_illinkPath = Path.Combine (Path.GetDirectoryName (taskDirectory), "net5.0", "illink.dll");
+				_illinkPath = Path.Combine (Path.GetDirectoryName (taskDirectory), "net6.0", "illink.dll");
 				return _illinkPath;
 			}
 			set => _illinkPath = value;

src/tools/illink/test/Mono.Linker.Tests/TestCasesRunner/TestCaseSandbox.cs

@@ -16,7 +16,7 @@ public class TestCaseSandbox
 
 		static NPath GetArtifactsTestPath ()
 		{
-			// Converts paths like /root-folder/linker/artifacts/bin/Mono.Linker.Tests/Debug/net5.0/illink.dll
+			// Converts paths like /root-folder/linker/artifacts/bin/Mono.Linker.Tests/Debug/net6.0/illink.dll
 			// to /root-folder/linker/artifacts/testcases/
 			string artifacts = Path.GetFullPath (Path.Combine (Path.GetDirectoryName (_linkerAssemblyPath), "..", "..", "..", ".."));
 			string tests = Path.Combine (artifacts, "testcases");