Fix resource leak on Test codes by copilot

https: //github.com/microsoft/pull/1825#discussion_r3303117760
Co-Authored-By: Copilot <198982749+Copilot@users.noreply.github.com>

Author: yuseok-kim-edushare

test/standalone/Garnet.test/ShutdownDataConsistencyTests.cs

@@ -138,7 +138,7 @@ public async Task CheckpointThenAofCommit_DataConsistencyTest()
             PopulateData();
 
             // Create CancellationTokenSource with a long timeout to prevent hanging indefinitely in case of issues during shutdown
-            var cts = new CancellationTokenSource(TimeSpan.FromMinutes(5));
+            using var cts = new CancellationTokenSource(TimeSpan.FromMinutes(5));
             TestContext.Progress.WriteLine($"Created CancellationTokenSource with 5 minute timeout for test shutdown");
 
             // Sequence: Checkpoint first, then AOF commit