Stop parenthesizing context managers on Python 3.9

[A5rocks]

Description

Discovered in python-trio/trio#3106 (comment), black is parenthesizing context managers for Python 3.9 despite that only officially landing in 3.10.

This isn't actually much of an issue as CPython 3.9 allows it and I assume PyPy does too, but it could technically be an issue and does mess things up with -X oldparser on 3.9.

Checklist - did you ...

• Add an entry in CHANGES.md if necessary?
• Add / update tests if necessary?
• Add new / update outdated documentation?

[JelleZijlstra]

This feels not worth it. We'd cause churn on projects that already run on 3.9 only. I'd rather stick with the new syntax only at this point.

[A5rocks]

This feels not worth it. We'd cause churn on projects that already run on 3.9 only. I'd rather stick with the new syntax only at this point.

Makes sense. The way it's implemented it doesn't actually downgrade already parenthesized context managers, if I remember correctly. Though that's obviously a bug that could maybe be treated as a feature.

[JelleZijlstra]

Thanks, but I'm going to reject this, especially since we've already released this style for a long time. Parenthesized context managers realistically work fine in Python 3.9; it's unlikely that anybody is actively using -X oldparser.