error[E0277]: `*mut pyo3::Python<'static>` cannot be shared between threads safely
 --> tests/ui/not_send.rs:4:22
  |
4 |     py.allow_threads(|| { drop(py); });
  |        ------------- ^^^^^^^^^^^^^^^^ `*mut pyo3::Python<'static>` cannot be shared between threads safely
  |        |
  |        required by a bound introduced by this call
  |
  = 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 Python<'static>>`
 --> $RUST/core/src/marker.rs
  |
  | pub struct PhantomData<T: ?Sized>;
  |            ^^^^^^^^^^^
note: required because it appears within the type `NotSend`
 --> src/impl_/not_send.rs
  |
  | pub(crate) struct NotSend(PhantomData<*mut Python<'static>>);
  |                   ^^^^^^^
  = note: required because it appears within the type `(&GILGuard, NotSend)`
note: required because it appears within the type `PhantomData<(&GILGuard, NotSend)>`
 --> $RUST/core/src/marker.rs
  |
  | pub struct PhantomData<T: ?Sized>;
  |            ^^^^^^^^^^^
note: required because it appears within the type `Python<'_>`
 --> src/marker.rs
  |
  | pub struct Python<'py>(PhantomData<(&'py GILGuard, NotSend)>);
  |            ^^^^^^
  = note: required for `&pyo3::Python<'_>` to implement `Send`
note: required because it's used within this closure
 --> tests/ui/not_send.rs:4:22
  |
4 |     py.allow_threads(|| { drop(py); });
  |                      ^^
  = note: required for `[closure@$DIR/tests/ui/not_send.rs:4:22: 4:24]` to implement `Ungil`
note: required by a bound in `pyo3::Python::<'py>::allow_threads`
 --> src/marker.rs
  |
  |     pub fn allow_threads<T, F>(self, f: F) -> T
  |            ------------- required by a bound in this associated function
  |     where
  |         F: Ungil + FnOnce() -> T,
  |            ^^^^^ required by this bound in `Python::<'py>::allow_threads`