As discussed in https://github.com/italia/publiccode.yml/issues/8, we should use the literals yes and no values for boolean values instead of true and false, since they are supported by the YAML spec:

A Boolean represents a true/false value. Booleans are formatted as English words (“true”/“false”,
“yes”/“no” or “on”/“off”) for readability and may be abbreviated as a single character “y”/“n” or “Y”/“N”.

source: https://yaml.org/type/bool.html

We should probably check whether the YAML library we use for serialization supports this.