Close #1095, update our actions' action dependencies to node 24

[plocket]

In this PR, I have:

• [NA] Added tests for any new features or bug fixes (if relevant)
• Added my changes to the CHANGELOG.md at the top, under the "Unreleased" section
• Ensured issues that this PR closes will be automatically closed

Reason for this PR

The actions that our actions depend on need to be updated to the latest version of node. Security and so on. Also may help us narrow down the causes for the inconsistent test GitHub+You failures we've been getting.

Links to any solved or related issues

Closes #1095

Any manual testing I have done to ensure my PR is working

As before, the manually-run Playground tests still only inconsistently pass.

More

Full text of the final squash commit:

Update action dependencies, close #1095

• checkout: https://github.com/actions/checkout#checkout-v7
• setup-node: Look into npm caching behavior more in https://github.com/actions/setup-node#breaking-changes-in-v5 and https://github.com/actions/setup-node#breaking-changes-in-v6
• setup-python: https://github.com/actions/setup-python/releases/tag/v6.0.0
• upload-artifact: https://github.com/actions/upload-artifact/releases v7.0.1 and some notes before that release show changes. Mostly moving to node v24, I think. Release docs are awkward and we can't link to a specific place in one document.
• download-artifacts: Maybe breaking change in https://github.com/actions/download-artifact/releases/tag/v5.0.0 about folder structure, but I think we're ok. Moving to v8. Release docs are awkward and we can't link to a specific place in one document.

[BryceStevenWilley]

LGTM!