Improve error message for string parsing

[pgundlach]

Describe the bug
When I try to read foo = bar to a string, I get an error:

1| foo = bar
 |       ~~~ incomplete number

I think this error message might lead to confusion.

To Reproduce

package main

import (
	"fmt"

	"github.com/pelletier/go-toml/v2"
)

func main() {
	doc := `foo = bar`
	type mystruct struct {
		Foo string
	}
	var mydata mystruct

	err := toml.Unmarshal([]byte(doc), &mydata)
	fmt.Println(err.(*toml.DecodeError).String())

}

Expected behavior
Since the library knows what kind of data I expect (Foo is a string), I'd expect an error message such as "could not parse string" or "quotes missing" or something like that.

Versions

• go-toml: github.com/pelletier/go-toml/v2 v2.0.7
• go: go1.20.1
• operating system: macOS

[pgundlach]

I guess this is a duplicate of #413 (comment)

[pelletier]

You're right, that's a duplicate of #413. I'll close this one, but will add a note on the other issue that we should look into using the type of the target to generate an error message.