Fix testLogsSlowInboundProcessing (elastic#121895)

This test creates an incorrectly-serialized handshake which cannot be
validated, and elastic#121747 made that validation compulsory. This test
corrects the serialization.

Closes elastic#121816

Author: DaveCTurner

server/src/test/java/org/elasticsearch/transport/InboundHandlerTests.java

@@ -290,7 +290,12 @@ public void testLogsSlowInboundProcessing() throws Exception {
             );
             BytesStreamOutput byteData = new BytesStreamOutput();
             TaskId.EMPTY_TASK_ID.writeTo(byteData);
-            TransportVersion.writeVersion(remoteVersion, byteData);
+            // simulate bytes of a transport handshake: vInt transport version then release version string
+            try (var payloadByteData = new BytesStreamOutput()) {
+                TransportVersion.writeVersion(remoteVersion, payloadByteData);
+                payloadByteData.writeString(randomIdentifier());
+                byteData.writeBytesReference(payloadByteData.bytes());
+            }
             final InboundMessage requestMessage = new InboundMessage(
                 requestHeader,
                 ReleasableBytesReference.wrap(byteData.bytes()),