[pre-commit.ci] pre-commit autoupdate

updates:
- [github.com/asottile/pyupgrade: v2.25.0 → v2.28.0](asottile/pyupgrade@v2.25.0...v2.28.0)
- [github.com/psf/black: 21.8b0 → 21.9b0](psf/black@21.8b0...21.9b0)

Author: pre-commit-ci[bot]

.pre-commit-config.yaml

@@ -5,7 +5,7 @@ repos:
       - id: end-of-file-fixer
       - id: trailing-whitespace
   - repo: https://github.com/asottile/pyupgrade
-    rev: v2.25.0
+    rev: v2.28.0
     hooks:
       - id: pyupgrade
         args: [--py37-plus, --keep-runtime-typing]
@@ -23,7 +23,7 @@ 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