Update run-tests.yml

[kudashevs]

Hello,

I would like to propose some improvements to the CI/CD workflow. This PR:

• adds support of PHP 8.1 (with all necessary exclusions)
• adds caching of composer dependencies (it is really optional, and if it doesn't seem reasonable I'll remove it)
• removes non-used PHP extensions (it speeds up a little bit)
• removes installation of the specific minimum versions of fzaninotto/faker and laravel/legacy-factories (it seems to work perfectly without the specific versions)
• adds installation of the specific minimum versions required by PHP 8.1 and Laravel 8.0 with prefer-lowest (I did it just in case. An explanation is below)

PS I'd prefer to totally exclude PHP 8.1 and Laralve 8.0 with prefer-lowest from processing (because it requires too many different minimum versions). However, the decision is up to you.

[cyrildewit]

Thanks @kudashevs. I appreciate your work on this.

PS I'd prefer to totally exclude PHP 8.1 and Laravel 8.0 with prefer-lowest from processing (because it requires too many different minimum versions). However, the decision is up to you.

I think it's always good to test it for multiple Laravel versions. Even if it requires some extra work.