Pin pre-commit versions

[max-sixty]

• Passes isort . && black . && mypy . && flake8
• User visible changes (including notable bug fixes) are documented in whats-new.rst

I had some issues with the version changing — this approach seems more explicit and less likely to cause hard-to-debug issues

[keewis]

To update we can use pre-commit autoupdate. Ideally, we would use the dependabot-like feature of the planned pre-commit CI which would automatically open PRs for us once there's a new version.

[max-sixty]

To update we can use pre-commit autoupdate. Ideally, we would use the dependabot-like feature of the planned pre-commit CI which would automatically open PRs for us once there's a new version.

Yes that'd be great; let's keep in touch with their progress there