error[E0277]: `*mut pyo3::Python<'static>` cannot be shared between threads safely
   --> tests/ui/not_send.rs:4:8
    |
4   |     py.allow_threads(|| { drop(py); });
    |        ^^^^^^^^^^^^^ `*mut pyo3::Python<'static>` cannot be shared between threads safely
    |
    = help: within `pyo3::Python<'_>`, the trait `Sync` is not implemented for `*mut pyo3::Python<'static>`
    = note: required because it appears within the type `PhantomData<*mut pyo3::Python<'static>>`
    = note: required because it appears within the type `impl_::not_send::NotSend`
    = note: required because it appears within the type `(&GILGuard, impl_::not_send::NotSend)`
    = note: required because it appears within the type `PhantomData<(&GILGuard, impl_::not_send::NotSend)>`
    = note: required because it appears within the type `pyo3::Python<'_>`
    = note: required because of the requirements on the impl of `Send` for `&pyo3::Python<'_>`
    = note: required because it appears within the type `[closure@$DIR/tests/ui/not_send.rs:4:22: 4:38]`
    = note: required because of the requirements on the impl of `Ungil` for `[closure@$DIR/tests/ui/not_send.rs:4:22: 4:38]`
note: required by a bound in `pyo3::Python::<'py>::allow_threads`
   --> src/marker.rs
    |
    |         F: Ungil + FnOnce() -> T,
    |            ^^^^^ required by this bound in `pyo3::Python::<'py>::allow_threads`