community/dotnet8-runtime: sets `sonameprefix`

Fixes #16629 (closed)

!74134 (merged) introduced recursive soname scanning, which broke the ability to install multiple dotnet major versions at once, as apk would think that they provided the same shared objects. By setting sonameprefix, we inform apk that different major versions provide different versions of those shared objects, fixing the issue.

Also backports a small change introduced with dotnet9-runtime so that dotnet8-runtime-artifacts does not depend on dotnet8-hostfxr.