fix: Bedework and GMX hints from the conformance run - #855

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/cache@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Summary report available at: https://github.com/python-caldav/caldav/actions/runs/43080839794#summary-130732652313