Apply suggestions from code review

Author: XuehaiPan

docs/advanced/classes.rst

@@ -1385,7 +1385,7 @@ You can do that using ``py::custom_type_setup``:
            type->tp_flags |= Py_TPFLAGS_HAVE_GC;
            type->tp_traverse = [](PyObject *self_base, visitproc visit, void *arg) {
                // https://docs.python.org/3/c-api/typeobj.html#c.PyTypeObject.tp_traverse
-   #if PY_VERSION_HEX >= 0x03090000  // Python 3.9
+   #if PY_VERSION_HEX >= 0x03090000
                Py_VISIT(Py_TYPE(self_base));
    #endif
                if (py::detail::is_holder_constructed(self_base)) {

tests/test_custom_type_setup.cpp

@@ -27,7 +27,7 @@ TEST_SUBMODULE(custom_type_setup, m) {
             type->tp_flags |= Py_TPFLAGS_HAVE_GC;
             type->tp_traverse = [](PyObject *self_base, visitproc visit, void *arg) {
         // https://docs.python.org/3/c-api/typeobj.html#c.PyTypeObject.tp_traverse
-#if PY_VERSION_HEX >= 0x03090000 // Python 3.9
+#if PY_VERSION_HEX >= 0x03090000
                 Py_VISIT(Py_TYPE(self_base));
 #endif
                 if (py::detail::is_holder_constructed(self_base)) {