Changes

feat(tikv/pd,pingcap/tidb,CSE): add bazel_pushdowntest to build matrix of real cluster test CI jobs (#3929)

Adds `bazel_pushdowntest` to the build matrix for real cluster test CI
jobs on trunk/feature branches and `release-nextgen-*` branches.

### Changes

- **`pipelines/pingcap/tidb/latest/ghpr_check2.groovy`** — Added
`run_real_tikv_tests.sh bazel_pushdowntest`
-
**`pipelines/pingcap/tidb/latest/pull_integration_realcluster_test_next_gen/pipeline.groovy`**
— Added `tests/realtikvtest/scripts/next-gen/run-tests.sh
bazel_pushdowntest`
-
**`pipelines/tidbcloud/cloud-storage-engine/dedicated/pull_integration_realcluster_test_next_gen/pipeline.groovy`**
— Added `tests/realtikvtest/scripts/next-gen/run-tests.sh
bazel_pushdowntest`
-
**`pipelines/tikv/pd/latest/pull_integration_realcluster_test_next_gen/pipeline.groovy`**
— Added `tests/realtikvtest/scripts/next-gen/run-tests.sh
bazel_pushdowntest`

No changes to `release-X.Y` branch CI jobs as specified.

- Fixes PingCAP-QE/ci#3928

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<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>add `bazel_pushdowntest` the build matrix of real cluster
test CI jobs</issue_title>
> <issue_description>The CI jobs likes:
> - `ghpr_check2`
> - `pull_integration_realcluster_test`
> - `pull_integration_realcluster_test_next_gen`
> 
> Do not change the CI jobs for `release-X.Y` branches, only for trunk
or feature branches or `release-nextgen-* branches`</issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>

- Fixes PingCAP-QE/ci#3928

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Co-authored-by: wuhuizuo <2574558+wuhuizuo@users.noreply.github.com>
 (commit: 153c748)