test: reduce flakiness of test-http-remove-header-stays-removed.js

Refs: nodejs/reliability#508
Refs: #46333
PR-URL: #46855
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

test/parallel/test-http-remove-header-stays-removed.js

@@ -20,7 +20,7 @@
 // USE OR OTHER DEALINGS IN THE SOFTWARE.
 
 'use strict';
-require('../common');
+const common = require('../common');
 const assert = require('assert');
 
 const http = require('http');
@@ -56,6 +56,14 @@ server.listen(0, function() {
     res.setEncoding('ascii');
     res.on('data', function(chunk) {
       response += chunk;
+      if (response === 'beep boop\n') {
+        setTimeout(function() {
+          // The socket should be closed immediately, with no keep-alive, because
+          // no content-length or transfer-encoding are used:
+          assert.strictEqual(res.socket.closed, true);
+          server.close();
+        }, common.platformTimeout(15));
+      }
     });
   });
 });