Issue #3635944: Add GitLab CI and kernel test coverage for the PDF Reader formatter

Closes #3635944

phpunit --testdox PHPUnit 11.5.57 by Sebastian Bergmann and contributors.

Runtime: PHP 8.3.36

..... 5 / 5 (100%)

Time: 00:02.612, Memory: 6.00 MB

Pdf Reader Formatter (Drupal\Tests\pdf_reader\Kernel\Plugin\Field\FieldFormatter\PdfReaderFormatter)

• ✔️ Google and ms viewers with data set "google"
• ✔️ Google and ms viewers with data set "ms"
• ✔️ Google viewer renders iframe
• ✔️ Embed renderer
• ✔️ Pdf js renderer

OK (5 tests, 45 assertions)