[pre-commit.ci] pre-commit autoupdate
[pre-commit.ci] pre-commit autoupdate

updates:
- https://gitlab.com/pycqa/flake8 → https://github.com/PyCQA/flake8
- [github.com/psf/black: 21.6b0 → 21.7b0](https://github.com/psf/black/compare/21.6b0...21.7b0)
- [github.com/pycqa/isort: 5.8.0 → 5.9.2](https://github.com/pycqa/isort/compare/5.8.0...5.9.2)

untitaker/vdirsyncer,untitaker/vdirsyncer,untitaker/vdirsyncer