Add PHP 8.1 tests
>>> [!note] Migrated issue
<!-- Drupal.org comment -->
<!-- Migrated from issue #3542950. -->
Reported by: [marcus_johansson](https://www.drupal.org/user/385947)
Related to !176
>>>
<h3 id="summary-problem-motivation">Problem/Motivation</h3>
<p>We saw in <span class="drupalorg-gitlab-issue-link project-issue-status-info project-issue-status-3"><a href="https://www.drupal.org/project/ai_agents/issues/3542301" title="Status: Closed (duplicate)">#3542301: Support PHP 8.1</a></span> that the PHP 8.1 standards where not followed and we missed this. While we do code review, these are things that static code analysis tools like PHPStan does and should do automatically.</p>
<p>Gitlab CI has a previous major that runs 10.5.x and PHP 8.1. We should turn this on.</p>
<h3 id="summary-proposed-resolution">Proposed resolution</h3>
<p>Turn on previous major in testing.<br>
Check for any failure and fix it.</p>
issue