Mailable $locale does not serialize when queuing

[alshenetsky]

• Laravel Version: 5.6.12
• PHP Version: 7.2.1
• Database Driver & Version: MySQL 5.5.5

Description:

Ability to set locale on Mailables was added in #23178
But there is a bug:
The $locale variable in Mailable class does not serializes.

Steps To Reproduce:

1. Make a Mailable class that implements ShouldQueue
2. Set mailable locale in instance constructor or build() method:

    /**
     * Build the message.
     *
     * @return $this
     */
    public function build()
    {
    	return $this->view('myview')->locale('lv');
    }

3. Let it be queued

And now, if we look into serialized job, we will see:

s:6:\"locale\";N;

When job starts running, instance does not receive locale.

	/**
	 * Send the invoice.
	 *
	 * @param  \Illuminate\Contracts\Mail\Mailer  $mailer
	 * @return void
	 */
	public function send(MailerContract $mailer)
	{
		dd($this->locale); // NULL
	
	}

[themsaid]

I can't replicate this, works fine for me.