testing/dotnet6-{build,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.