test, http: add regression test for keepalive 'end' event

This test covers a regression where 'end' was not emitted in the case
of keepalive requests without parsing the full body.

PR-URL: #29263
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/parallel/test-http-server-keepalive-end.js

@@ -0,0 +1,29 @@
+'use strict';
+
+const common = require('../common');
+const { createServer } = require('http');
+const { connect } = require('net');
+
+const server = createServer(common.mustCall((req, res) => {
+  req.on('end', common.mustCall());
+  res.end('hello world');
+}));
+
+server.unref();
+
+server.listen(0, common.mustCall(() => {
+
+  const client = connect(server.address().port);
+
+  const req = [
+    'POST / HTTP/1.1',
+    `Host: localhost:${server.address().port}`,
+    'Connection: keep-alive',
+    'Content-Length: 11',
+    '',
+    'hello world',
+    ''
+  ].join('\r\n');
+
+  client.end(req);
+}));