All dependencies must be prefixed with the project name, for example "drupal:"

Kindly review patch.

As stated in the comment right above the dependency declaration, omitting the project name is an intentional workaround for how packages.drupal.org doesn't handle declaring a dependency on a module from a distribution very well. As seen in https://www.drupal.org/project/farm_forest/issues/3190919 → this is a workaround suggested by one of the maintainers of packages.drupal.org → .
Also, if packages.drupal.org would handle it right, the dependency with project id would have to be `farm:farm_map`, the standalone farm_map project → is no longer maintained, and the version updated to farmOS v2 (D8+) is now included directly in the farmOS → distribution.