When I change the signature of the function, it still works normally #891

package main

import (
	"fmt"
	"time"

	"github.com/expr-lang/expr"
)

func main() {
	env := map[string]any{
		// no error return
		"foo": func(string, ...string) time.Time { return time.Time{} },
		"str": "",
	}
	prog, err := expr.Compile(`foo(str)`, expr.Env(env))
	if err != nil {
		panic(err)
	}
	// define changed
	env["foo"] = func(s string, layout ...string) (time.Time, error) {
		fmt.Println("called")
		return time.Now(), nil
	}
	_, err = expr.Run(prog, env)
	if err == nil {
		panic(fmt.Sprintf("expected error for change the function signature.but no error return."))
	}
}