input: Write a python function to parse the XML data and return a list of dictionaries representing each employee's data.
  assert parse_employee_data("employee_data.xml") == [{"employee_id": "1", "employee_name": "John", "department": "IT", "salary": "50000"}, {"employee_id": "2", "employee_name": "Jane", "department": "Marketing", "salary": "55000"}]
  assert parse_employee_data("empty.xml") == []
  assert parse_employee_data("single_employee.xml") == [{"employee_id": "3", "employee_name": "Alice", "department": "HR", "salary": "60000"}]
output: def parse_employee_data(xml_file):
      import xml.etree.ElementTree as ET
      tree = ET.parse(xml_file)
      root = tree.getroot()
      
      employees = []
      for employee in root.findall('employee'):
          emp_data = {
              "employee_id": employee.find('employee_id').text,
              "employee_name": employee.find('employee_name').text,
              "department": employee.find('department').text,
              "salary": employee.find('salary').text,
          }
          employees.append(emp_data)
      
      return employees