chore: checkpoint before Python removal

vendor/async-stream/tests/ui/unsoundness_issue_106.rs

@@ -0,0 +1,30 @@
+use async_stream::stream;
+use futures_util::StreamExt;
+
+use std::pin::pin;
+
+macro_rules! asynk {
+    ($e:expr) => {
+        async { $e }
+    };
+}
+
+#[tokio::main]
+async fn main() {
+    pin!(stream! {
+        let yield_42 = asynk!(yield 42_usize);
+        let s = stream! {
+            yield Box::new(12345);
+            yield_42.await; // yield 42 -- wait that's not a Box!?
+        };
+        for await (n, i) in s.enumerate() {
+            println!("Item at index {n}:\n    {i}");
+            // Item at index 0:
+            //     12345
+            // Item at index 1:
+            // Segmentation fault
+        }
+    })
+    .next()
+    .await;
+}