pwn.ssh can't work well on server with python2

## Version

`pwntools==4.12.0`

## Description

When I try to use `pwn.ssh` to connect to a server (let's call it SA), the process gets stuck and keeps waiting indefinitely.

Upon investigation, I discovered that in `ssh.py`, line 945, the script being executed on SA is as follows:

```python
script = r"""
#!/usr/bin/env python
import os, sys, ctypes, resource, platform, stat
```

This script does not explicitly specify the use of Python 3. When I logged into SA, I found that `/usr/bin/env python` indeed calls Python 2, not Python 3.

To resolve this, I suggest renaming `python` to `python3` in this script.