chore: checkpoint before Python removal

vendor/async-stream/tests/ui/unsoundness_issue_107.rs

@@ -0,0 +1,23 @@
+use async_stream::stream;
+use futures_util::StreamExt;
+
+use std::pin::pin;
+
+#[tokio::main]
+async fn main() {
+    let mut outer = vec![];
+    {
+        let v = vec![0; 10];
+        let v_ref = &v;
+        let mut s = pin!(stream! {
+            for x in v_ref {
+                yield x
+            }
+        });
+        while let Some(x) = s.next().await {
+            outer.push(x);
+        }
+    };
+    // use-after-free
+    println!("{outer:?}"); // […garbage allocator internals…, 0, 0, 0]
+}