CI: add musl build

[igaw]

As we are constantly breaking musl based builds, we should add a CI build for this.

See #660 #2561 #2562

[MaisenbacherD]

If it's not super urgent you can assign me to this :) I have a few tasks on my list before I can address this.

[igaw]

No, not really urgent. Just created issue so we don't forget about it. Thanks!