Fix oversight (fixes https://github.com/mitsuba-renderer/mitsuba3/blob/ede09ae55dd747a008f74f1a5f4889f371029ae4/src/core/tests/test_python.py#L90)

Author: rwgk

include/pybind11/detail/common.h

@@ -606,7 +606,8 @@ struct from_python_policies {
         : rvpp(return_value_policy::automatic_reference), convert(true), none(true) {}
 
     // NOLINTNEXTLINE(google-explicit-constructor)
-    from_python_policies(bool convert, bool none = true) : convert(convert), none(none) {}
+    from_python_policies(bool convert, bool none = true)
+        : rvpp(return_value_policy::automatic_reference), convert(convert), none(none) {}
 
     // NOLINTNEXTLINE(google-explicit-constructor)
     from_python_policies(const return_value_policy_pack &rvpp)