Adds #5554 locale for acceptance notifications and checkin/out emails

[Godmartinz]

This uses the locale of the $assigned_user for acceptance emails and checkin/out
The system's locale is used for alert emails and cc emails.

This fires the Mail::to() twice in the checkoutable listener. This is the best way I could think of to handle the different locales for this process.

Fixes: #5554

[snipe]

Looks like you've got some failing tests here:

FAILED Tests\Feature\Notifications\Email\EmailNotificationsToAdminAlertE…
The expected [App\Mail\CheckoutAssetMail] mailable was not sent.
Failed asserting that false is true.

[Godmartinz]

Tests are fixed. We no longer fire off an attached cc() to the mailable, and it fires an additional email for different localization. Updated the test accordingly.