input: Write a function to convert a person's name and age into an XML string.
  assert person_to_xml("John Doe", 30) == '<?xml version="1.0" ?>\n<person>\n    <name>John Doe</name>\n    <age>30</age>\n</person>'
  assert person_to_xml("Jane Smith", 25) == '<?xml version="1.0" ?>\n<person>\n    <name>Jane Smith</name>\n    <age>25</age>\n</person>'
  assert person_to_xml("Alice Brown", 40) == '<?xml version="1.0" ?>\n<person>\n    <name>Alice Brown</name>\n    <age>40</age>\n</person>'
output: def person_to_xml(name, age):
      return f'<?xml version="1.0" ?>\n<person>\n    <name>{name}</name>\n    <age>{age}</age>\n</person>'