### Bug Description the `license:` field cannot be a [license expression](https://packaging.python.org/en/latest/glossary/#term-License-Expression) which does not allow to accurately depict the license of the main components of the rock. my use case: https://github.com/canonical/rockcraft/issues/978 [rust and cargo are dual licensed under MIT or Apache-2.0](https://www.rust-lang.org/policies/licenses) and the rock also includes the gcc tolchain [which is licensed under GPL-3.0]( https://gcc.gnu.org/onlinedocs/libstdc++/manual/license.html) ### To Reproduce `license: (MIT OR Apache-2.0) AND GPL-3.0` ### Environment n/a ### rockcraft.yaml ```yaml n/a ``` ### Relevant log output ```shell 2025-09-25 18:48:56.052 Bad rockcraft.yaml content: 2025-09-25 18:48:56.053 - license (MIT OR Apache-2.0) AND GPL-3.0 not valid. It must be either 'proprietary' or in SPDX format. (in field 'license') ```