[Enhancement] Generate mpy artifacts only on changed source

[xs5871]

Is your feature request related to a problem? Please describe. We started building mpy artifacts to download for every PR merge. Those builds are also triggered for documentation or board code updates.

Describe the solution you'd like Look into using a changed files GH action (see #800) to generate mpy artifacts only when the python source tree has changed.

[rrotter]

Looks like this is the solution:

https://stackoverflow.com/questions/70902669/github-action-trigger-a-job-only-when-there-is-a-change-in-particular-director

[xs5871]

Thanks for the reminder. We actually have a pending PR #857 that does that (well not yet, hence pending).