Laravel 9 and PHP 8.1 Support with CI

[clnt]

Description

• Composer.json updated to support both Laravel 8/PHP 7.4 and Laravel 9/PHP 8.1 so it can be tagged as a non breaking change (change to just support Laravel 9 and 8.1 if you want to release on a 3.0.0 tag).
• GitHub Actions workflow added. https://github.com/clnt/laravel-feature/actions

Motivation and context

Package does not install on a Laravel 9 install with PHP 8.1 due to composer restraints.

How has this been tested?

New GitHub Actions CI workflow added which runs a matrix running PHPUnit on both PHP 7.4 and PHP 8.1 (travis could be removed)
Left the code I use for codecov commented out if you wish to use it over scrutinizer otherwise action step will need updating to use.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING document.
• My pull request addresses exactly one patch/feature.
• I have created a branch for this patch/feature.
• Each individual commit in the pull request is meaningful.
• I have added tests to cover my changes.
• If my change requires a change to the documentation, I have updated it accordingly.

[cbaigorri]

Can these changes be limited to just the ones in the composer.json?
I would also like to use this package on Laravel 9/PHP 8.1.

[francescomalatesta]

Thanks a lot for your effort @clnt 🚀