Update from Node 20 to Node 24

[maureenlholland]

Also adds Sass-related deps to dependabot ignore settings. They can be removed from this setting at the same time Sass is unpinned.

If this changeset needs to go into the FXC codebase, please add the WMO and FXC label.

One-line summary

Significant changes and points to review

Issue / Bugzilla link

#16910
Twinned with mozmeao/springfield#1180

Testing

Successful integration test run: https://github.com/mozilla/bedrock/actions/runs/25670980573

Successful integration test (May 26, 2026) with no Node 20 warnings: https://github.com/mozilla/bedrock/actions/runs/26446688757

[janriokrause]

r+ Looks good to me. Integration tests ran successfully, but I didn't test anything manually.

[stevejalim]

If you're happy, I'm happy @maureenlholland

Question (blocking): how come package-lock.json didn't change when the headline node version has? Do the the JS deps need recompiling locally using node 24, changing the package-lock.json, I'm assuming, as part of this upgrade?

[maureenlholland]

@stevejalim I don't think so. I ran npm install locally with node v24.15.0 and saw no package-lock changes.

But I don't think the v4 setup node is doing what we want. Will move to v5 and check integration tests again.

[maureenlholland]

Integration test run for v6: https://github.com/mozilla/bedrock/actions/runs/26104915009
confirmed running Node 24

[maureenlholland]

It is probably worth updating these other actions in this PR too:
Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected:

• actions/upload-artifact@v4
• slackapi/slack-github-action@v1.25.0

[maureenlholland]

https://github.com/mozilla/bedrock/actions/runs/26170334565
good news: the node 20 warnings are gone
bad news: slackapi is broken

need to fix slack (probably missing breaking changes required with major update)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.34%. Comparing base (e8e2529) to head (058de56).
⚠️ Report is 13 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17168      +/-   ##
==========================================
+ Coverage   82.31%   82.34%   +0.03%     
==========================================
  Files         181      181              
  Lines        9692     9709      +17     
==========================================
+ Hits         7978     7995      +17     
  Misses       1714     1714              

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