Update pre-commit Black hook to mirror repo

It's ~2x faster as it installs the mypyc-compiled wheel.

Author: adamchainz

.pre-commit-config.yaml

@@ -40,7 +40,7 @@ repos:
   hooks:
   - id: pyupgrade
     args: [--py38-plus]
-- repo: https://github.com/psf/black
+- repo: https://github.com/psf/black-pre-commit-mirror
   rev: 23.9.1
   hooks:
   - id: black