tour: add example for together named returns and defer functions

[salihdev0]

Named Returns Context: https://go.dev/tour/basics/7

Defer Functions Context: https://go.dev/tour/flowcontrol/12

Named returns are much more valuable with the value. There are also nice use cases where they can be used together in real life. An example can be added where the two are together, as follows:

package main

import (
	"errors"
	"fmt"
)

func main() {
	if err := runDatabaseTransaction(); err != nil {
		fmt.Println("Error:", err)
	}
}

func runDatabaseTransaction() (err error) {
	defer func() {
		if err != nil {
			fmt.Println("an error occurred:", err)
			// Handle the error, e.g., rollback the transaction
		}
	}()
	err = errors.New("index out of range") // Simulating an error
	if err != nil {
		return err
	}
	return nil
}