test: remove Windows skipping of http keepalive request GC test

Remove code to skip Windows in test-http-server-keepalive-req-gc. The
test now works reliably on Windows (I think).

PR-URL: #29354
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>

test/parallel/test-http-server-keepalive-req-gc.js

@@ -5,11 +5,6 @@ const onGC = require('../common/ongc');
 const { createServer } = require('http');
 const { connect } = require('net');
 
-if (common.isWindows) {
-  // TODO(addaleax): Investigate why and remove the skip.
-  common.skip('This test is flaky on Windows.');
-}
-
 // Make sure that for HTTP keepalive requests, the req object can be
 // garbage collected once the request is finished.
 // Refs: https://github.com/nodejs/node/issues/9668