chore: use 2x faster black mirror (#170)

Committed via https://github.com/asottile/all-repos

Author: henryiii

.pre-commit-config.yaml

@@ -34,7 +34,7 @@ repos:
   - id: trailing-whitespace
 
 # Black, the code formatter, natively supports pre-commit
-- repo: https://github.com/psf/black
+- repo: https://github.com/psf/black-pre-commit-mirror
   rev: 23.7.0
   hooks:
   - id: black