Upgrade gh actions using Node 20

[serendipty01]

In e2e.yaml, actions/cache (v4.3.0) and actions/upload-artifact (v5.0.0) use Node 20.

Action Run: https://github.com/roostorg/coop/actions/runs/28888597152
Warning:

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830, actions/upload-artifact@330a01c490aca151604b8cf639adc76d48f6c5d4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Github Blogpost on deprecation

Solution:

Upgrade versions of the affected github actions

actions/cache → v5.0.0
actions/upload-artifact → v6.0.0

Open questions:

1. Check other workflows as well
2. Can dependabot be used for version upgrade ? and should we use it ?