[chore] ci: move actions off the deprecated node 20 runtime

[arpit-bruno]

BRU-4718

GitHub has deprecated Node 20 for Actions so every run warns and forces our Node 20 actions onto Node 24. This bumps each action to the lowest major version that runs on Node 24. Versions only, nothing else changes.

- checkout v4 → v5
- setup-node v4 → v5
- cache v4 → v5
- upload-artifact v4 → v6
- download-artifact v4 → v7
- mise-action v2 → v4
- paths-filter → v4.0.3, still pinned by SHA
- test-reporter is already on Node 24, unchanged

Release notes show no breaking change for how we use them:

• setup-node only auto-caches when package.json has a packageManager field and we have none
• download-artifact only changed paths for downloads by artifact ID, and we download by pattern

[changeset-bot]

⚠️ No Changeset found

Latest commit: 4c22d6c

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

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[arpit-bruno]

after #99 merge, will merge release/v0.5.0 into this branch and bump the new checkout@v4 in changeset.yml to v5 so nothing is left on node 20