Bump GitHub actions Node24

[gioelemo]

Description

• Bump all GitHub Actions to their latest major versions to resolve Node.js 20 deprecation warnings
• Node.js 20 will be forced off GitHub Actions runners on June 2, 2026 and fully removed on September 16, 2026 (changelog)

Version bumps

Action	Old	New
actions/checkout	v4	v6
actions/setup-python	v4/v5	v6
actions/upload-artifact	v4	v7
actions/download-artifact	v4	v8

pre-commit/action remains at v3.0.1 as it is the latest release. It internally uses actions/cache@v4 (Node.js 20), with no plan to update in the future: pre-commit/action#241.

Affected workflows

• lint.yaml
• pre-commit.yaml
• test.yml
• docs-main.yml
• docs-release.yml
• publish-pypi.yaml

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files
• I have run ruff check . and ruff format
• I have run mypy .
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Reviewer Checklist:

• The content of this PR brings value to the community. It is not too specific to a particular use case.
• The tests and checks pass (linting, formatting, type checking). For a new problem, double check the github actions workflow to ensure the problem is being tested.
• The documentation is updated.
• The code is understandable and commented. No large code blocks are left unexplained, no huge file. Can I read and understand the code easily?
• There is no merge conflict.
• The changes are not breaking the existing results (datasets, training curves, etc.). If they do, is there a good reason for it? And is the associated problem version bumped?
• For a new problem, has the dataset been generated with our slurm script so we can re-generate it if needed? (This also ensures that the problem is running on the HPC.)
• For bugfixes, it is a robust fix and not a hacky workaround.

[gioelemo]

conventional-commits is failing due to the wrong structure/message of my last commit, sorry.
I can also open a PR for EngiOpt when needed.