[CI] Generate full baseline upon PHPStan failure

Problem/Motivation

When a PHPStan job fails for core, a new baseline file artifact is generated. However, that is an incremental one (i.e. contains entries only for the NEW failures).

It would be more helpful to get a full baseline file so to copypaste it in the mr branch as is.

See https://drupal.slack.com/archives/CGKLP028K/p1730242123771039 for some insights.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet