Changes

feat(prow-jobs/pingcap/tidb): enable auto trigger and set as required for `pull-unit-test-next-gen` job (#3770)

Now the job is passed:

![img_v3_02qg_36d270db-4205-416d-8316-6af0616e0a6g](https://github.com/user-attachments/assets/13045810-b754-4b06-aec6-759206ced0dd)

Also refactor presubmits to use jenkins_job anchor
 (commit: e90288a)