chore(deps): bump actions/cache from 4 to 6 - #25

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: dependabot/fetch-metadata@d7267f607e9d3fb96fc2fbe83e0af444713e90b7. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/