env GO111MODULE=on

go mod edit -godebug 'http2debug=2'
cmp go.mod go.mod.edit.want1

go mod edit -json
cmp stdout go.mod.edit.want2
-- go.mod --
module foo

go 1.25.0
-- go.mod.edit.want1 --
module foo

go 1.25.0

godebug http2debug=2
-- go.mod.edit.want2 --
{
	"Module": {
		"Path": "foo"
	},
	"Go": "1.25.0",
	"GoDebug": [
		{
			"Key": "http2debug",
			"Value": "2"
		}
	],
	"Require": null,
	"Exclude": null,
	"Replace": null,
	"Retract": null,
	"Tool": null,
	"Ignore": null
}