infra: Add CI/CD action to verify make skels

[teodutu]

Many tasks (and all in the future) use make skels with this Makefile [1] and this script [2] to generate the skeleton code for each task in the support/ folder from the one in solution/.

A new CI/CD action is required. It should be given a list of paths in the repo where the script should run make skels and print where there were errors. The action should fail if any errors are encountered or pass otherwise.

[1] https://github.com/cs-pub-ro/operating-systems/blob/main/chapters/compute/processes/drills/tasks/mini-shell/Makefile
[2] https://github.com/cs-pub-ro/operating-systems/blob/main/chapters/compute/processes/drills/tasks/mini-shell/generate_skels.py