Support Laravel 9.

[abrardev99]

This PR adds the new Laravel 9.x version support to the package.

[stancl]

Ideally, the matrix options would be named, like L8 and L9 instead of the 8.x that's displayed on the screenshot below.

So perhaps we do need to use the matrix (to provide a name for each variant), but we don't need to specify anything other than the Laravel version.

[abrardev99]

Ideally, the matrix options would be named, like L8 and L9 instead of the 8.x that's displayed on the screenshot below.

Yeah, I renamed it accordingly.