[pre-commit.ci] pre-commit autoupdate (#786)
[pre-commit.ci] pre-commit autoupdate (#786)

updates:
- [github.com/psf/black: 21.4b2 → 21.5b1](https://github.com/psf/black/compare/21.4b2...21.5b1)
- [github.com/PyCQA/flake8: 3.9.1 → 3.9.2](https://github.com/PyCQA/flake8/compare/3.9.1...3.9.2)

Co-authored-by: pre-commit-ci[bot] <3ea08453efb076ca910552532a53973a6527df40@users.noreply.github.com>
amolenaar/gaphor,amolenaar/gaphor