fix type error when converting GADM id

[doneachh]

Closes # (if applicable).

Changes proposed in this Pull Request

Checklist

• [ ] I tested my contribution locally and it seems to work fine.
• [ ] Code and workflow changes are sufficiently documented.
• [ ] Newly introduced dependencies are added to envs/environment.yaml and envs/environment.docs.yaml.
• [ ] Changes in configuration options are added in all of config.default.yaml, config.tutorial.yaml, and test/config.test1.yaml.
• [ ] Changes in configuration options are also documented in doc/configtables/*.csv and line references are adjusted in doc/configuration.rst and doc/tutorial.rst.
• [ ] A note for the release notes doc/release_notes.rst is amended in the format of previous release notes, including reference to the requested PR.

[doneachh]

@davide-f Could be probably linked with the other issue (with len(x)) as i used the same config for the run

[doneachh]

@davide-f #326 doesnt fix this here. should we leave it like this or fix it as well with the layer id here? Would probably prefer to make it this way as we dont have redundant code then :)

[davide-f]

Answered on the other PR, feel free to ping me in discord if I lose it here