Add allow_update_branch to .asf.yaml

[Dev-iL]

Changes

Enable the allow_update_branch setting for the project.

Either true to always allow a pull request head branch that is behind its base branch to be updated even if it is not required to be up to date before merging, or false otherwise.
https://docs.github.com/en/rest/repos/repos?apiVersion=2022-11-28

How I tested this

Notes

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.