testing/dotnet6-build: add testsuite, patch update

testing/dotnet6-build/APKBUILD

testing/dotnet6-build/build_musl-build-fix.patch

testing/dotnet6-build/check_alpine-support.patch

testing/dotnet6-build/command-line-api_fix-musl-build.patch

testing/dotnet6-build/installer_musl-build-fix.patch

testing/dotnet6-build/installer_portable-runtime-id.patch

...force-microsoftnetcoreilasmpackageruntimeid-as-musl.patch

testing/dotnet6-build/runtime_lld-fix.patch

...g/dotnet6-build/runtime_x86-64-use-system-libunwind.patch

testing/dotnet6-build/sdk_portable-runtime-id.patch

testing/dotnet6-build/sdk_telemetry-optout.patch