ci: upgrade actions/upload-artifact in Lighthouse workflow (v2 deprecated)

[jimmyandrade]

Context

The Lighthouse workflow fails on GitHub Actions because it uses a deprecated action.

Failed run (before fix): https://github.com/multei/web/actions/runs/29500476368/job/87627853033

This request has been automatically failed because it uses a deprecated version of
`actions/upload-artifact: v2`.
Learn more: https://github.blog/changelog/2024-02-13-deprecation-notice-v1-and-v2-of-the-artifact-actions/

File: .github/workflows/lighthouse.yml

Goal

Update the Lighthouse workflow to currently supported GitHub Actions and restore a green job for the deprecated-action failure.

Suggested scope

• Bump actions/upload-artifact from v2 to a supported major (v4).
• Review other actions in the same workflow (actions/checkout@v7, treosh/lighthouse-ci-action@12.6.2) and upgrade if deprecated or incompatible.
• Confirm the Lighthouse job no longer fails on deprecated actions at “Set up job”.
• Confirm the lighthouseresults upload step is configured (upload-artifact@v4); end-to-end artifact publish still blocked until LHCI collect succeeds (see follow-up).

Acceptance criteria

• Lighthouse workflow no longer fails on “Set up job” due to a deprecated action.
• Lighthouse results artifact step remains in the workflow (actions/upload-artifact@v4 → lighthouseresults).
• A recent workflow run fails only on a real Lighthouse/site regression, not toolchain. (Verified: run 29500972827 — Set up job ✅, LHCI collect fails with CHROME_INTERSTITIAL_ERROR against https://multei.com.br)

Notes

• Deprecation changelog: https://github.blog/changelog/2024-02-13-deprecation-notice-v1-and-v2-of-the-artifact-actions/
• Also scanned .github/workflows/: no other upload-artifact@v1/v2. nodejs.yml still uses actions/checkout@v2 / setup-node@v1 (out of scope here).
• Follow-up: production URL triggers Chrome interstitial during LHCI collect — track separately if needed.

[jimmyandrade]

Done

Shipped on main:

• actions/upload-artifact@v2 → @v4
• actions/checkout@v2 → @v7
• treosh/lighthouse-ci-action@v3 → @12.6.2

Verification: Lighthouse run 29500972827

• Set up job / checkout succeed (deprecated-action failure fixed)
• LHCI collect still fails with CHROME_INTERSTITIAL_ERROR on https://multei.com.br (site/runtime, not the artifact action)