Update pinned action versions for Node.js 24 compatibility

[oxyc]

Summary

GitHub Actions runners will force Node.js 24 by default starting June 2, 2026 and remove Node.js 20 entirely on September 16, 2026. The following actions pinned in setup/action.yml are running on Node.js 20:

Action	Current SHA	Current Version	Latest
actions/setup-node	49933ea	v4	v6.3.0
actions/cache	0057852	v4.3.0	v5.0.4
shivammathur/setup-php	44454db	v2	v2.37.0

actions/checkout is already on v6.0.2 (Node.js 24 compatible).

Actions needed

• Update setup/action.yml: bump actions/setup-node to v6, actions/cache to v5, shivammathur/setup-php to latest v2
• Check all other composite actions and reusable workflows for stale pins
• Pin to full commit SHAs of the new versions

References

• https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/