Existem várias maneiras de o pandas salvar dados csv.

O primeiro:

import os
import pandas as pd

path = 'data/train/'
img_label_list=[]
testList = os.listdir(path)
for file in testList:
    label='aa'
    img_label_list.append([file, label])

df1 = pd.DataFrame(data=img_label_list,
                      columns=['id', 'label'])
df1.to_csv('result.csv',index=False)

o segundo

import os
import pandas as pd

path = 'data/train/'
img_list=[]
lable_list=[]
testList = os.listdir(path)
for file in testList:
    img_list.append(file)
    label='aa'
    lable_list.append(label)

img_label_list2 = list(zip(img_list, lable_list))
df3 = pd.DataFrame(data=img_label_list2,
                      columns=['filepath', 'label'])
df3.to_csv('result.csv',index=False)

O terceiro:

import os
import pandas as pd

path = 'data/train/'
img_list=[]
lable_list=[]
testList = os.listdir(path)
for file in testList:
    img_list.append(file)
    label='aa'
    lable_list.append(label)

df = pd.DataFrame({
    
    "filename": img_list, "label": lable_list})
df.to_csv('result.csv',index=False)