Refactor: consolidate testing into docker-buildx.yml

Refactor: consolidate testing into docker-buildx.yml This change removes the separate test workflow and integrates the testing steps directly into the main docker-buildx workflow. This ensures that images are built, tested, and only pushed if tests pass. - Deletes .github/workflows/test-drupal.yml - Updates .github/workflows/docker-buildx.yml to include test setup, execution, and cleanup steps. - Uses `load: true` for the test build step to verify the image locally. - Retains multi-platform build and push for the final step upon success. - Updates triggers to run on push to main and pull requests. Co-authored-by: hussainweb <1040271+hussainweb@users.noreply.github.com>