Fix phpunit, phpstan, phpcs, eslint and cspell pipeline tests

Problem/Motivation

Automated test pipelines are currently failing on the 8.x-3.x branch.

This makes it harder to review, validate, and merge changes against the branch, because contributors cannot reliably tell whether a pipeline failure has been caused by their own change or by an existing issue in the branch/test setup.

The failing pipelines need to be investigated so that the branch has a reliable baseline again.

Steps to reproduce

1. Open a merge request or issue fork targeting the 8.x-3.x branch.
2. Run the GitLab pipeline.
3. Review the pipeline test report.
4. Confirm that one or more jobs fail independently of the specific change being proposed.

Proposed resolution

Investigate the failing pipeline jobs on the 8.x-3.x branch and make the required changes so that the test suite passes reliably again.

Remaining tasks

1. Review recent failing pipelines on the 8.x-3.x branch.
2. Identify the failing tests.
3. Confirm that the failure is branch-wide rather than specific to one merge request.
4. Apply the required fix.
5. Rerun the pipeline.
6. Confirm all required jobs pass.

User interface changes

None.

API changes

None.

Data model changes

None.