[dotnet] Fix packaging problems

Author: diemol

dotnet/private/nuget.bzl

@@ -72,7 +72,7 @@ def _stage_files_for_packaging(ctx, staging_dir):
         relative_dest_file = _get_relative_destination_file(src_file)
         src_list.append((src_file, relative_dest_file))
         if (ctx.attr.create_symbol_package):
-            symbol_file = dep.default_runfiles.files.to_list()[0]
+            symbol_file = dep[DefaultInfo].files.to_list()[0]
             relative_dest_symbol_file = _get_relative_destination_file(symbol_file)
             src_list.append((symbol_file, relative_dest_symbol_file))