Run tests for PHP 7.4, 8.0, and 8.1.1 via GitHub Actions

[marcusmoore]

Description

This PR introduces a workflow to run our phpunit test suite via GitHub Actions for our supported PHP versions: 7.4, 8.0, and 8.1.1.

[what-the-diff]

PR Summary

• Implementation of Automated Testing Workflow
  This update introduces a new file (.github/workflows/tests.yml) which serves as the backbone for our automated testing procedure on GitHub. A significant improvement towards maintaining code quality on a regular basis.

• Triggering of Workflow
  Any changes or additions to the 'master' and 'develop' branches will now kick off this automated process.

• Inclusion of Job Named 'Tests'
  We've included a job called 'tests', operating on the latest Ubuntu version. This job ensures all new changes live up to our testing standards.

• Integration with MySQL Database
  The job includes making use of a MySQL database to handle the testing data management.

• Testing Multiple PHP Versions
  The workflow can handle testing with various PHP versions. It makes our testing protocol more adaptable and covers wider PHP environments.

• Enhanced Testing Steps
  The testing procedure involves several steps, from setting up the PHP version and repository checkout, to getting the Composer cache directory and caching it. This update also implements copying of .env.testing.example to .env and .env.testing, installing dependencies, generating a key, setting directory permissions, and running tests using PHPUnit.

• Utilizing Specific Environment Variables
  The procedure utilizes specific environment variables – ensuring our tests work in a controlled and stable environment.