Run pre-commit in separate workflow

[mathbunnyru]

Several reasons for this change:

• PRs like this shouldn't trigger docker build. [pre-commit.ci] pre-commit autoupdate #1339
• A bit faster CI (1 minute)
• Unfortunately, we can't fully rely on pre-commit.ci, because we use Docker-based linter and docker is not available in pre-commit.ci

[mathbunnyru]

Related to #1203

[mathbunnyru]

@consideRatio we can't merge to the master if there is something in the master which is not yet built.
This will cause errors.
The reason for that is that in the docker builds we clone the wiki in the beginning, and at the end of the build update the wiki.
And in between, we build the images (it's a long step that takes more than 30 minutes now).
And then there will be two commits in the docs which change the docs in a different way.
So, the second build will not update wiki (manifests).
And so the CI will fail

[consideRatio]

Wooops ah, did i merge this PR and trigger a workflow running alongside another workflow triggered via some other PR that got merged independently?

[mathbunnyru]

Yes, #1340 was merged 16 minutes before you merged, and that's why there are two simultaneous runs right now.

[mathbunnyru]

And, the first merge is done.
Your merge will probably fail (because of the docs).

[mathbunnyru]

@consideRatio I updated the description of the situation and created a mitigation PR.
The build failed as I described: https://github.com/jupyter/docker-stacks/runs/2717699712