Make CI enforce pre-commit clean code (#1096) * pre-commit: Enforce pre-commit clean code via CI * ci.yml: Resolve duplication of isort and yapf By now pre-commit is already running these. * ci.yml: Move flake8 to pre-commit * README.rst: Add CI status badge for workflow "Run pre-commit" * README.rst: Fix link for CI workflow "YAPF" (ci.yml)