Timeout error for GitHub action CacheNotebooks

The GitHub action [repo2docker-action](https://github.com/jupyterhub/repo2docker-action) seems to have a maximum time allowed of 900s to trigger mybinder (implemented [here](https://github.com/jupyterhub/repo2docker-action/blob/86cbba650927d185d7cee256eb48d0a7eeb38906/trigger_binder.sh#L8)).
So, our action fails with the timeout error `curl: (28) Operation timed out after 900000 milliseconds with 423286 bytes received`.

A question about the possibility of adjusting the time limit can be found in this [issue](https://github.com/jupyterhub/repo2docker-action/issues/88).

Start by reading trigger_binder.sh in repo2docker-action at the linked line and the referenced repo2docker-action issue 88. Confirm whether the 900-second limit can be configured or changed upstream, then determine whether Trixi.jl needs an actionable workflow change. Done means the timeout cause and a supported resolution are established.

Written by the indexing model from the issue text.