[Test] Use stream.next instead of setAutoRead in test (elastic#115063)

For a more realistic simulation.

modules/transport-netty4/src/internalClusterTest/java/org/elasticsearch/http/netty4/Netty4IncrementalRequestHandlingIT.java

@@ -175,12 +175,16 @@ public void testClientConnectionCloseMidStream() throws Exception {
             var handler = ctx.awaitRestChannelAccepted(opaqueId);
             assertBusy(() -> assertNotNull(handler.stream.buf()));
 
-            // enable auto-read to receive channel close event
-            handler.stream.channel().config().setAutoRead(true);
             assertFalse(handler.streamClosed);
 
-            // terminate connection and wait resources are released
+            // terminate client connection
             ctx.clientChannel.close();
+            // read the first half of the request
+            handler.stream.next();
+            // attempt to read more data and it should notice channel being closed eventually
+            handler.stream.next();
+
+            // wait for resources to be released
             assertBusy(() -> {
                 assertNull(handler.stream.buf());
                 assertTrue(handler.streamClosed);