LibWeb: Enable callbacks in chunk steps for ReadableStreamDefaultTee

We enqueue a microtask for this readable stream AO, and the methods that
we call from the chunk steps manipulate promises. As such, we need to
enable callbacks for the entire microtask's temporary execution
context.

Userland/Libraries/LibWeb/Streams/AbstractOperations.cpp

@@ -401,7 +401,7 @@ public:
     {
         // 1. Queue a microtask to perform the following steps:
         HTML::queue_a_microtask(nullptr, JS::create_heap_function(m_realm->heap(), [this, chunk]() {
-            HTML::TemporaryExecutionContext execution_context { Bindings::host_defined_environment_settings_object(m_realm) };
+            HTML::TemporaryExecutionContext execution_context { Bindings::host_defined_environment_settings_object(m_realm), HTML::TemporaryExecutionContext::CallbacksEnabled::Yes };
 
             auto controller1 = m_params->branch1->controller()->get<JS::NonnullGCPtr<ReadableStreamDefaultController>>();
             auto controller2 = m_params->branch2->controller()->get<JS::NonnullGCPtr<ReadableStreamDefaultController>>();