Changes

chore(pipeline) next-gen migrate to GCP (#4377)

## Summary
Migrate
`tidbcloud/cloud-storage-engine/dedicated/pull_integration_realcluster_test_next_gen`
to GCP runtime path, and keep migration-specific hotfixes scoped to this
job.

## Why Temporary Skips
- These two cases are currently noisy/flaky under realcluster migration
validation (resource pressure / cluster bootstrap instability), and they
block signal for infra migration readiness.
- The skip is explicitly temporary and scoped to this job only.

verify in
https://prow.tidb.net/jenkins/job/tidbcloud/job/cloud-storage-engine/job/dedicated/job/pull_integration_realcluster_test_next_gen/14/
 (commit: 4b455e9)