Changes

fileserver: migrate tikv/tikv artifact downloads to OCI registry (#4267)

Removes all `fileserver.pingcap.net` references from `tikv/tikv`
pipelines, replacing artifact fetches with OCI-based downloads via
`hub-zot.pingcap.net/mirrors/hub`.

## Changes

- **`pull_unit_test.groovy` (11 files)** — Removed unused
`FILE_SERVER_URL` env var across all branches (latest, release-6.1 →
release-9.0-beta); the variable was declared but never consumed in these
pipelines.

- **`pull_integration_test.groovy` (6 files: latest, release-6.1, 6.5,
7.1, 7.5, 8.1)** — Migrated artifact preparation stage from
`fetchAndExtractArtifact` to `download_pingcap_oci_artifact.sh`:

  ```groovy
  // Before
  environment { FILE_SERVER_URL = 'http://fileserver.pingcap.net' }
  // ...
  component.fetchAndExtractArtifact(FILE_SERVER_URL, 'pd', ...)
  component.fetchAndExtractArtifact(FILE_SERVER_URL, 'tikv', ...)
  component.fetchAndExtractArtifact(FILE_SERVER_URL, 'tidb', ...)

  // After
final OCI_TAG_PD = component.computeArtifactOciTagFromPR('pd',
REFS.base_ref, REFS.pulls[0].title, 'master')
final OCI_TAG_TIKV = component.computeArtifactOciTagFromPR('tikv',
REFS.base_ref, REFS.pulls[0].title, 'master')
final OCI_TAG_TIDB = component.computeArtifactOciTagFromPR('tidb',
REFS.base_ref, REFS.pulls[0].title, 'master')
  environment { OCI_ARTIFACT_HOST = 'hub-zot.pingcap.net/mirrors/hub' }
  // ...
  container('utils') {
sh "${WORKSPACE}/scripts/artifacts/download_pingcap_oci_artifact.sh
--pd=${OCI_TAG_PD} --tikv=${OCI_TAG_TIKV} --tidb=${OCI_TAG_TIDB}"
  }
  ```

- **`pod-pull_integration_test.yaml` (6 files)** — Added `utils`
container (`ghcr.io/pingcap-qe/cd/utils/release:v2025.10.12-7-gfdd779c`)
to each integration test pod spec, providing the `oras` tooling required
by the download script.

<!-- START COPILOT ORIGINAL PROMPT -->



<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>fileserver: migrate artifacts for tikv/tikv</issue_title>
> <issue_description>Replace fileserver.pingcap.net usage for tikv/tikv
with OCI artifacts in a standard registry.
> 
> Acceptance criteria:
> - No fileserver.pingcap.net references in jobs/pipelines for tikv/tikv
> - Artifacts pulled via OCI registry with documented paths
> </issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>



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- Fixes PingCAP-QE/ci#4212

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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>
Co-authored-by: wuhuizuo <wuhuizuo@126.com>
 (commit: 85e98b4)