Fe1-Web CI is slow / node_modules are not cached

[pierluca]

Description (Actual behavior)

The action Setup npm dependencies takes >90s on each run.

Expected behavior

Setup npm dependencies should be extremely fast and only slow when dependencies change, i.e. when the package-lock.json file has changed and new dependencies need to be installed and the cache file re-created.

Possible root cause

Currently, there's an action called Setup node cache in the CI definition for Fe1-Web, but it only caches the node environment and not the node_modules directory.
It might also be worthwhile to look at whether Setup expo action could be cached, as it takes ~30s.

How to reproduce

Open any PR and look at the execution of the Fe1-Web actions.
e.g. https://github.com/dedis/popstellar/runs/5336261406?check_suite_focus=true#logs

Version & Environment

This bug was reproduced on:

• Commit: 6fb168e
• Environment: GitHub Actions

Workaround

Being patient :-)

Impact

It takes a longer time to obtain feedback from GitHub actions (>5min instead of ~3min)