github action step that ensures that scss was compiled into css for all PRs

[jkowalleck]

@gnikonorov proposed to have a github action step that ensures that scss was compiled into css for all PRs.

see also the discussion here: #385 (comment)

[gnikonorov]

Thanks for opening this @jkowalleck. Can you update the link in the issue description? It seems broken

[jkowalleck]

updated link in description to aworking one.