[Test] Use stream.next instead of setAutoRead in test

For a more realistic simulation.

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

@@ -175,10 +175,11 @@ 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);
 
+            handler.stream.next(); // read the first half of the request
+            handler.stream.next(); // attempt to read more data and it should notice channel being closed eventually
+
             // terminate connection and wait resources are released
             ctx.clientChannel.close();
             assertBusy(() -> {