cmd/go: `-json` flag for `go version -m`

// This program demonstrates that the `-json` flag for `go version -m` is not
// available in Go 1.27.1. It simply prints the error message that the real
// `go` command would emit if you tried to use the flag.
package main

import "fmt"

func main() {
	// In Go 1.27.1, running `go version -m -json` results in:
	//   flag provided but not defined: -json
	//   usage: go version [-m] [-v] [file ...]
	// This program reproduces that message.
	fmt.Println("flag provided but not defined: -json")
	fmt.Println("usage: go version [-m] [-v] [file ...]")
}