Squash improper_ctypes warnings on nightly

Lots more warnings are showing up on nightly compilers due to a recent
change. I've opened rust-lang/rust#66373 on the compiler side for this
as well.

crates/misc/py/src/lib.rs

@@ -1,3 +1,5 @@
+#![allow(improper_ctypes)]
+
 use crate::import::into_instance_from_obj;
 use crate::instance::Instance;
 use crate::memory::Memory;