If there is a to set to an array e.g. (`to [amd64,arm64]`) and not single value (e.g. `to amd64`), grammar processor does not handle it correctly. The value is accepted, but it's never matched. I think it should either raise validation error if array is not an accepted value, or match architecture correctly. Here is an example failing UT: https://github.com/canonical/craft-grammar/commit/cc15ba9cc65b46b5451f541b640b46a7a1277a4a