Not 100% compliant with YAML 1.2

[bfabio]

We state that

publiccode.yml MUST be a UTF-8 encoded and SHOULD be a YAML 1.2 document, using YAML 1.1 is deprecated.
https://yml.publiccode.tools/schema.core.html#encoding

But the library we use now says:

Specifically, v3 of the yaml package:

• Supports YAML 1.1 bools (yes/no, on/off) as long as they are being decoded into a typed bool value. Otherwise they behave as a string. Booleans in YAML 1.2 are true/false only.
• Supports octals encoded and decoded as 0777 per YAML 1.1, rather than 0o777 as specified in YAML 1.2, because most parsers still use the old format. Octals in the 0o777 format are supported though, so new files work.
  https://github.com/yaml/go-yaml?tab=readme-ov-file#compatibility

Depends on #195

[bfabio]

Fixed by #331, which replaces gopkg.in/yaml.v3 with github.com/goccy/go-yaml.

yes/no/on/off are now parsed as strings, not booleans. When assigned to a typed bool field, goccy returns a type error instead of silently coercing them.

0777 is still parsed as octal (511), matching yaml.v3 behavior. This is technically YAML 1.1, but there are no integer fields in the schema so it has no practical effect.