Show "About case studies" block only to authenticated users

This block will have to move into drupalorg_block() to put that access check in code. An alternative is look at r4032login module or other way to make access denied pages more friendly, which would put this in the infrastructure queue.

Why does this need code? Core blocks have role-based access checks ever since 5.0. See #18018: Block visibility by role. That was my very first ever core patch, in fact. ;)

I forgot that existed. Done.