Fix CI pipeline, PHPStan errors and the ddev setup

Problem/Motivation

The pipeline is red on both branches, and the ddev setup on 3.x no longer works.

On 2.x, .gitlab-ci.yml does not set DRUPAL_CORE, so the tests run against the latest core while the branch declares ^9 || ^10. The module cannot be installed, so every functional and kernel test aborts, and the unit tests fail on PHPUnit 11.

On 3.x, PHPStan reports 17 errors, mostly calls to user_load_by_name(), deprecated in drupal:11.4.0.

The ddev-drupal-contrib addon is pinned at 1.0.0-rc23 while 1.1.3 is out. The project symlinking and ddev phpstan are broken, and .ddev/config.contrib.yaml hardcodes DRUPAL_CORE=^11.

Proposed resolution

Pin the core version on 2.x, fix the PHPStan errors on 3.x, and reinstall the ddev addon.

Remaining tasks

• Fix whichever 2.x unit tests still fail once the core version is pinned.
• The read-only property errors have no clean fix while PHP 8.3 is supported, so they may need a baseline entry.

User interface changes

None.

API changes

None.

Data model changes

None.