[2/N] Use pyupgrade --py39-plus to improve code
Author: cyyever
Pull request: yes

# What does this PR do?
Because refactoring according to Python 3.9 syntax involves lots of Python files, the changes have been divided into a series of PRs for easier review. This is follow-up of #36843 
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Comments:
Hi 👋, thank you for opening this pull request! The pull request is converted to draft by default. When it is ready for review, please click the `Ready for review` button (at the bottom of the PR page).

@Rocketknight1 Ready

Merged! I'm happy to accept the remaining changes in one huge PR if that's easier for you, btw