Fix cDAC dump test build: add TestInfrastructure using directive

Co-authored-by: rcj1 <77995559+rcj1@users.noreply.github.com>

Author: Copilot

src/native/managed/cdac/tests/DumpTests/DacDbi/DacDbiApproxTypeHandleDumpTests.cs

@@ -5,6 +5,7 @@
 using System.Collections.Immutable;
 using Microsoft.Diagnostics.DataContractReader.Contracts;
 using Microsoft.Diagnostics.DataContractReader.Legacy;
+using Microsoft.Diagnostics.DataContractReader.TestInfrastructure;
 using Microsoft.DotNet.XUnitExtensions;
 using Xunit;