fs: wait for in-flight ops before cloning File (#5803)

If there is an ongoing operation on a file, wait for that to complete
before performing the clone in `File::try_clone`. This avoids a race
between the ongoing operation and any subsequent operations performed on
the clone.

Fixes: #5759

tokio/src/fs/file.rs

@@ -399,6 +399,7 @@ impl File {
     /// # }
     /// ```
     pub async fn try_clone(&self) -> io::Result<File> {
+        self.inner.lock().await.complete_inflight().await;
         let std = self.std.clone();
         let std_file = asyncify(move || std.try_clone()).await?;
         Ok(File::from_std(std_file))