Tests: close the 2.0.1 ref-list probe's method (it did not compile at the previous commit)

OldReaderRefListProbe.cs is staged into the 2.0.1 tree by old-reader-refusal.sh and is not part of this tree's build; its method
lacked a closing brace at fd9bbaf4, which the gate's 2.0.1-reader stage reported.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/vectors/document-variants-c2a/old-reader-probes/OldReaderRefListProbe.cs

@@ -2,7 +2,6 @@
 using System;
 using System.IO;
 using System.Linq;
-using System.Text.Json;
 using System.Threading.Tasks;
 using GameCult.Caching;
 using GameCult.Caching.MessagePack;
@@ -60,5 +59,6 @@ namespace GameCult.Caching.Tests
             {
                 File.Delete(copy);
             }
+        }
     }
 }