input: Write a function to generate an HTML form with a submit button that sends information to a specified Python program. The function should take the action URL of the Python program as an input and return the HTML code for the form.
  assert generate_html_form("action.py")=='<form action="action.py" method="post"><input type="submit" value="Submit"></form>'
  assert generate_html_form("process.py")=='<form action="process.py" method="post"><input type="submit" value="Submit"></form>'
  assert generate_html_form("submit.py")=='<form action="submit.py" method="post"><input type="submit" value="Submit"></form>'
output: def generate_html_form(action_url):
      return f'<form action="{action_url}" method="post"><input type="submit" value="Submit"></form>'