zoneinfo should probably be not in locale domain

This came up while https://gitlab.com/freedesktop-sdk/freedesktop-sdk/-/merge_requests/25294 zoneinfo files are not locales

https://github.com/apache/buildstream/blob/6c06e1b117a13076cbccbd6f6a2b5f833322ba60/src/buildstream/data/projectconfig.yaml#L165-L167