input: Write a python function to generate a pie chart image from a list of data.
  assert generate_pie_chart([30, 30, 20, 20]) is not None
  assert generate_pie_chart([15, 25, 35, 25]) is not None
  assert generate_pie_chart([10, 40, 30, 20]) is not None
output: def generate_pie_chart(data):
      import matplotlib.pyplot as plt
      import io
      from PIL import Image
      
      fig, ax = plt.subplots()
      ax.pie(data, autopct='%1.1f%%', startangle=90)
      ax.axis('equal')
  
      buf = io.BytesIO()
      plt.savefig(buf, format='png')
      plt.close(fig)
      buf.seek(0)
      image = Image.open(buf)
      
      return image