[5.0] Allow Stability To Be Passed To Workbench

As a Developer
When working on a dev version of Laravel and making a Laravel Package using workbench 
I would like to still use php artisan workbench without getting the error that matching stability level not found so I can continue making Laravel packages for a project even when using a dev version of Laravel

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This way Workbench allows the stability option and more importantly continues to work when 
in transitions like L4 to L5.

You need to update this in both stubs, not just one of them.