Remove drush dependency for core GitLab CI pipelines

Problem/Motivation

Per #3437726-6: Fix issues with Validatable config job → , core's new "Validatable config" pipeline job depends on drush. The drush is always moving, and there's currently no version that can be installed with core 11.x. So all such pipeline jobs are failing right now.

I asked about it in Slack, where @catch said "We should open an issue to get rid of the drush dependency if we can." This is that issue.

Steps to reproduce

Proposed resolution

Don't depend on drush/drush for Drupal core gitlab-ci.yml jobs.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet