astro/{calcmysky,stellarium}: update both ports to the latest versions

It's unfortunate transition time when they cannot be updated separately,
not at least without some ugly patching.

Make Stellarium use static release tarball instead of the generated by
GitHub one. While currently it does not win us much, next version will
be additionally offering smaller .tar.xz distfile which we'll switch to
more easily.

Enforce Qt5 build for now. While Stellarium and its dependencies are
Qt6-ready, providing correct and coherent flavors for all of them is
too much work for little gain. Everyone should be using Qt5 anyways.

PR: 266915