chore: Upgrade baseline python function version to 3.13

[ShadowCat567]

Description of changes

Upgrades baseline python version used for the function category to 3.13.
This should not affect existing customers, but new customers who create python lambda functions with amplify will be using 3.13 as a baseline version instead of 3.8.

Issue #, if available

Description of how you validated changes

Newly create lambda function using python 3.13:

Newly created function in lambda using 3.13

Checklist

• PR description included
• yarn test passes
• Tests are changed or added
• Relevant documentation is changed or added (and PR referenced)
• New AWS SDK calls or CloudFormation actions have been added to relevant test and service IAM policies
• Pull request labels are added

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