Migrate bs-callout to GlAlert in …/unmet_prerequisites_block.vue

What does this MR do?

Updates the Bootstrap callout to GlAlert for job failures.

Reviewer: To get the alert to appear without triggering a failure, remove the v-if="hasUnmetPrerequisitesFailure" line from gitlab/app/assets/javascripts/jobs/components/job_app.vue and view a job under CI / CD > Jobs.

Screenshots

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

N/A

Security

N/A

Related to #242028 (closed)