remote: Flush to stdin when writing to sftp 2 (#42126)

https://github.com/zed-industries/zed/pull/42103#issuecomment-3498137130

Release Notes:

- N/A *or* Added/Fixed/Improved ...

crates/remote/src/transport/ssh.rs

@@ -306,7 +306,7 @@ impl RemoteConnection for SshRemoteConnection {
                     use futures::AsyncWriteExt;
                     let sftp_batch = format!("put -r {src_path_display} {dest_path_str}\n");
                     stdin.write_all(sftp_batch.as_bytes()).await?;
-                    drop(stdin);
+                    stdin.flush().await?;
                 }
 
                 let output = child.output().await?;