test(audience-http): accept HttpClient's TaskCanceledException wrap

SendBatchAsync_CallerCancelled_Throws was asserting the exact type
`OperationCanceledException` via `Assert.ThrowsAsync`. HttpClient
internally catches the OCE our mock throws and rethrows it as
`TaskCanceledException` (a subclass), so `ThrowsAsync` — which is
exact-type — missed.

Switch to `CatchAsync<OperationCanceledException>`, which accepts the
whole cancellation family. This is what we actually want to assert:
"cancellation propagated", not "HttpClient happens to throw this exact
subclass".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ImmutableJeffrey

src/Packages/Audience/Tests/Runtime/Transport/HttpTransportTests.cs

@@ -415,7 +415,10 @@ public void SendBatchAsync_CallerCancelled_Throws_DoesNotDeleteOrRecordFailure()
             using var cts = new CancellationTokenSource();
             cts.Cancel();
 
-            Assert.ThrowsAsync<OperationCanceledException>(
+            // CatchAsync (not ThrowsAsync) because HttpClient re-wraps our mock's
+            // OperationCanceledException as TaskCanceledException before rethrowing.
+            // We want to assert the cancellation *family*, not a specific subclass.
+            Assert.CatchAsync<OperationCanceledException>(
                 async () => await transport.SendBatchAsync(cts.Token));
 
             Assert.AreEqual(1, _store.Count(), "cancelled send must not delete the batch");