how to handle pandas columns with list items?

Question

import pandas as pd
test = pd.DataFrame({"report_number":[['21-10541', '21-6300'],[ '20-55506']],
 "date": ['2021-06-03','2021-06-04']})

I have the above dataset, and as you can see the report number column sometimes contains multiple report numbers in a single row. using test a dataframe as the input, I want to create an output dataframe as follows where each row is a single report number, and the date corresponding to that report number.

Desired Ouput

    |   report_number       |    date      |
    |    21-1054            |    2021-06-03|
    |    21-6300            |    2021-06-03|
    |    20-55506           |    2021-06-04|

I tried the following

def f(x):
    if len(x['report_number'])>1:
        for i in x['report_number']:
            return(i,x['date'])
    else:
        return (x['report_number'],x['date'])

test1.apply(f,axis=1)

But it does not seem to work