Address GitHub Actions warnings re: node.js 16

[khaeru]

GitHub Actions has started warning about deprecation of Node.js 16, for instance here:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3, actions/setup-python@v4, ts-graphviz/[email protected], r-lib/actions/setup-r@v2, actions/cache@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

This PR updates 'first-party' actions as suggested:

• actions/checkout v3 → v4
• actions/setup-python v4 → v5

Per third-party actions:

• codecov/codecov-action: v4 is available with Node.js 20: https://github.com/codecov/codecov-action/releases
• pre-commit/action: pending Update action checkout, cache, python pre-commit/action#188 it seems this action is actually abandoned and won't receive updates. One alternate approach is to inline the few steps; see e.g. Release v24.2.5 transport-data/tools#14.
• r-lib/actions/setup-r: Update actions to use Node.js 20 r-lib/actions#792.
• ts-graphviz/setup-graphviz: pending Update from Node 16 to Node 20 ts-graphviz/setup-graphviz#558

Other housekeeping:

• Replace black with ruff format for code style (Swap black for ruff format in code style/pre-commit message_ix#772).
• Tweak the "publish" CI workflow:
  • Remove the trigger for pushes to main (analogous to Save minutes by avoiding duplicate test runs #515).
  • Add concurrency: setting to prevent 2 conflicting jobs being started on a release (one triggered by the release event, one by the tag creation event).

How to review

Read the diff and note that the CI checks all pass.

PR checklist

• Continuous integration checks all ✅
• Add or expand tests; coverage checks both ✅
• Add, expand, or update documentation. N/A, CI changes only
• Update release notes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8a2aa91) 98.9% compared to head (8679d00) 98.9%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #517     +/-   ##
=======================================
- Coverage   98.9%   98.9%   -0.1%     
=======================================
  Files         44      44             
  Lines       4795    4795             
=======================================
- Hits        4744    4743      -1     
- Misses        51      52      +1     

Files	Coverage Δ
ixmp/tests/test_model.py	100.0% <ø> (ø)

... and 1 file with indirect coverage changes

[glatterf42]

Looks good to me :)
Do we use Node.js anywhere else, i.e. should we bump checkout and setup-python in the other repos as well?
There are at least some warnings for message-ix-models as well.

[khaeru]

Yes, we'll need to make similar changes for each repo in the stack. Please let me know if you'd like me to handle certain of those.