Windows CI jobs fail due to 403 error downloading Alpine Linux is setup-wsl step #2107

This step is recently failing in all Windows jobs:

It seems this may have first occurred in #2106. But it is not due to any changes there, as can be confirmed by rerunning the workflow. This resembles the old resolved issue Vampire/setup-wsl#77, but I'm not sure if the cause is actually related. I've opened a new issue Vampire/setup-wsl#82 for it.

I think we can solve this here by putting the distribution back to Debian (or Ubuntu). When doing so, the extra Alpine-specific code for installing bash should be removed. I'll do this unless some way of getting Alpine to work becomes apparent soon.