Fix test threading (#31669)

Content.IntegrationTests/Tests/Buckle/BuckleDragTest.cs

@@ -34,7 +34,11 @@ public sealed class BuckleDragTest : InteractionTest
         Assert.That(pullable.BeingPulled, Is.False);
 
         // Strap the human to the chair
-        Assert.That(Server.System<SharedBuckleSystem>().TryBuckle(sUrist, SPlayer, STarget.Value));
+        await Server.WaitAssertion(() =>
+        {
+            Assert.That(Server.System<SharedBuckleSystem>().TryBuckle(sUrist, SPlayer, STarget.Value));
+        });
+
         await RunTicks(5);
         Assert.That(buckle.Buckled, Is.True);
         Assert.That(buckle.BuckledTo, Is.EqualTo(STarget));