Python 3: Remove xfail comment (#26182)

diff --git a/tools/wptserve/tests/functional/test_handlers.py b/tools/wptserve/tests/functional/test_handlers.py
index 8c0e020..261bf3b 100644
--- a/tools/wptserve/tests/functional/test_handlers.py
+++ b/tools/wptserve/tests/functional/test_handlers.py
@@ -195,7 +195,6 @@
         assert resp.read() == b""
 
 
-@pytest.mark.xfail((3,) <= sys.version_info < (3, 6), reason="wptserve only works on Py2")
 class TestJSONHandler(TestUsingServer):
     def test_json_0(self):
         @wptserve.handlers.json_handler