Update lamabda runtime version due to "AWS Lambda end of support for Python 3.8"

[nabe1653]

Hi there. First, Thank you for development about good package. I've been helped everytime.

Today I've got the mail from AWS about AWS Lambda end of support for Python 3.8; It said AWS will finish support at October 14, 2024. So I check dependence functions then deployed cdk function has python3.8 runtime and main branch code has runtime: lambda.Runtime.PYTHON_3_8, line.

Could you update runtime version? Thank you.