[pavog]

This PR splits the CI workflow into a unit test job and an integration test job.

Unit tests

• Run on every push and pull request, on PHP 8.4 and 8.5.
• PHP is set up with pcov, and the tests write a clover report to coverage.xml.

Integration tests

• The integration tests send requests to the live Modrinth API. They now run in a separate job on PHP 8.5, only on pushes to master and when the workflow is started manually.
• Pull requests no longer run them, so a slow or unavailable API does not block a PR.

phpunit.xml.dist

• Coverage is only collected for src/Client. The generated code in src/Api and src/Model is not tested directly.