[pre-commit.ci] pre-commit autoupdate

updates:
- [github.com/psf/black: 21.8b0 → 21.9b0](psf/black@21.8b0...21.9b0)

Author: pre-commit-ci[bot]

.pre-commit-config.yaml

@@ -11,7 +11,7 @@ repos:
     hooks:
       - id: isort
   - repo: https://github.com/psf/black
-    rev: "21.8b0"
+    rev: "21.9b0"
     hooks:
       - id: black
   - repo: https://github.com/PyCQA/flake8