Fix poisoning issue with existing marker (#17527)

Author: NikolaMilosavljevic

src/SourceBuild/content/eng/tools/tasks/Microsoft.DotNet.SourceBuild.Tasks.LeakDetection/MarkAndCatalogPackages.cs

@@ -155,6 +155,7 @@ public override bool Execute()
                     }
                     File.Delete(p.ItemSpec);
                     File.Move(poisonedPackagePath, p.ItemSpec);
+                    Directory.Delete(packageTempPath, true);
                 }
             }