[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

@@ -1,7 +1,7 @@
 exclude: doc/en/example/py2py3/test_py2.py
 repos:
 -   repo: https://github.com/psf/black
-    rev: 21.8b0
+    rev: 21.9b0
     hooks:
     -   id: black
         args: [--safe, --quiet]