Add support for Laravel 11 (#81)

* Add Laravel 11 dependency

* Remove/replace broken links

* Tweak package versions

* Attempt to support PHPUnit v10 and v8 simultaneously

* Drop support of PHPUnit v8

Dropping support of PHPUnit v8 means dropping support of PHP 7.2 which means dropping support of Laravel v6 and v7

* Update workflow

* Update tests and upgrade phpunit.xml

* Update upgrade guide

* Attempt to use newer GH actions

* Configure Codecov

* Formatting

* Remove unneeded test case

IDE Helper-related issue was patched in v2.9.1, which only supported Laravel 7+. Since we dropped older Laravel versions, we can remove this.

@see barryvdh/laravel-ide-helper#627

* Improve phrasing

* Whoops

* Rearrange

Laravel 9 support