input: Write a python function to repeat a given string a specified number of times.
  assert repeat_string("Hello!", 3) == "Hello!Hello!Hello!"
  assert repeat_string("abc", 2) == "abcabc"
  assert repeat_string("Python", 4) == "PythonPythonPythonPython"
output: def repeat_string(s: str, n: int) -> str:
      return s * n