Fix timestamp comparison in federated tracing test

Parse ISO 8601 timestamps using Carbon before comparing them.
Protobuf serialization may produce timestamps with varying microsecond
precision (e.g., `.619Z` vs `.619236Z`), which causes string comparisons
to fail because `619236Z` is alphabetically less than `619Z`.

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

Author: spawnia

tests/Integration/Tracing/FederatedTracingExtensionTest.php

@@ -4,6 +4,7 @@
 
 use GraphQL\Error\DebugFlag;
 use Illuminate\Contracts\Config\Repository;
+use Illuminate\Support\Carbon;
 use Nuwave\Lighthouse\Federation\FederationServiceProvider;
 use Nuwave\Lighthouse\Tracing\FederatedTracing\FederatedTracing;
 use Nuwave\Lighthouse\Tracing\FederatedTracing\Proto\Trace;
@@ -129,11 +130,11 @@ public function testAddFtv1ExtensionMetaToBatchedResults(): void
         $trace1Data = $this->decodeFtv1Record($result->json('0.extensions.ftv1'));
         $trace2Data = $this->decodeFtv1Record($result->json('1.extensions.ftv1'));
 
-        $startTime1 = $trace1Data['startTime'];
-        $endTime1 = $trace1Data['endTime'];
+        $startTime1 = Carbon::parse($trace1Data['startTime']);
+        $endTime1 = Carbon::parse($trace1Data['endTime']);
 
-        $startTime2 = $trace2Data['startTime'];
-        $endTime2 = $trace2Data['endTime'];
+        $startTime2 = Carbon::parse($trace2Data['startTime']);
+        $endTime2 = Carbon::parse($trace2Data['endTime']);
 
         // Guaranteed by the usleep() in $this->resolve()
         $this->assertGreaterThan($startTime1, $endTime1);