Changes

Migrate Jenkins cron-triggered integration test to Prow periodic (#4264)

The `periodics_integration_test` job for `pingcap/tidb` (latest/master)
was self-scheduling via a Jenkins cron trigger (`0 * * * *`), bypassing
Prow and causing potential duplication with centrally-managed
scheduling.

## Changes

- **`prow-jobs/pingcap/tidb/latest-periodics.yaml`** — Added Prow
periodic entry for `pingcap/tidb/latest/periodics_integration_test`
using `agent: jenkins`, retaining the original hourly schedule:
  ```yaml
  - name: pingcap/tidb/latest/periodics_integration_test
    agent: jenkins
    labels:
master: "0" # Jenkins master instance to run this job (0 = default
master)
    decorate: false
    cron: "0 * * * *" # every hour
    extra_refs:
      - org: pingcap
        repo: tidb
        base_ref: master
  ```

- **`jobs/pingcap/tidb/latest/periodics_integration_test.groovy`** —
Removed `pipelineTriggers { triggers { cron{ spec('0 * * * *') } } }`
block. The Jenkins job definition is retained so Prow can invoke it;
scheduling ownership now lives exclusively in Prow.

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<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>Migrate Jenkins cron jobs to Prow periodic</issue_title>
> <issue_description>Identify Jenkins scheduled/periodic jobs and move
them to Prow periodic jobs to avoid multi-Jenkins duplication.
> 
> Acceptance criteria:
> - Jenkins cron triggers removed or disabled
> - Equivalent Prow periodic jobs added
> - Schedule ownership documented
> </issue_description>
> 
> <agent_instructions>the jenkins job defined in `jobs/`
folder.</agent_instructions>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



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- Fixes PingCAP-QE/ci#4207

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wuhuizuo <2574558+wuhuizuo@users.noreply.github.com>
 (commit: 8c47148)