error[E0277]: `Rc<i32>` cannot be sent between threads safely
   --> tests/ui/pyclass_send.rs:4:1
    |
4   | #[pyclass]
    | ^^^^^^^^^^ `Rc<i32>` cannot be sent between threads safely
    |
    = help: within `NotThreadSafe`, the trait `Send` is not implemented for `Rc<i32>`
note: required because it appears within the type `NotThreadSafe`
   --> tests/ui/pyclass_send.rs:5:8
    |
5   | struct NotThreadSafe {
    |        ^^^^^^^^^^^^^
note: required by a bound in `ThreadCheckerStub`
   --> src/impl_/pyclass.rs
    |
    | pub struct ThreadCheckerStub<T: Send>(PhantomData<T>);
    |                                 ^^^^ required by this bound in `ThreadCheckerStub`
    = note: this error originates in the attribute macro `pyclass` (in Nightly builds, run with -Z macro-backtrace for more info)