Int map keys incorrectly marshaled as string

[herczegzsolt]

Describe the bug
Whenever go-yaml encounters a map with int key, it marshals it like it had a string key. This makes it incompatible with itself.

To Reproduce

This is very easy to reproduce with even a simple map[int]string.

import (
	"fmt"

	"github.com/goccy/go-yaml"
)

func main() {
	f := make(map[int]string)
	f[1] = "one"
	f[3] = "three"
	enc, _ := yaml.Marshal(f)
	fmt.Printf("%s\n", enc)
	var g map[int]string
	err := yaml.Unmarshal(enc, &g)
	fmt.Printf("%v\n", err)
	fmt.Printf("%v\n", g)
}

Playground link is here: https://go.dev/play/p/OWQPOj_ECBP

Expected behavior
I expect that map[int]string would be encoded as 1: "one" not as "1":"one"
I also expect that yaml.Unmarshal can handle without errors whatever output yaml.Marshal has created.

If you do nothing else than replace the import from github.com/goccy/go-yaml to gopkg.in/yaml.v3, the example code would work as expected.

Screenshots
Please run the code on Go Playground :-)

Version Variables

• Go version: 1.24.1
• go-yaml's Version: v1.15.13
  But I think it affects all available versions.

Additional context
I tried to workaround this by using a MarshalYAML()([]byte,error) method on the map key type, but even if I return the byte slice directly, it is converted to string.