CI unit test jobs fail to produce bazel.xml junit report

## Problem

CI unit test jobs (`ghpr_unit_test`) fail to produce `bazel.xml` junit report file, causing junit artifact collection to be skipped.

## Root Cause

In `build/jenkins_unit_test.sh` and `build/jenkins_unit_test_ddlargsv1.sh`, the `bazel_collect` tool is installed (line 26) but never invoked after `make bazel_ci_test` completes. The tool is needed to generate the local junit XML from Bazel's build event protocol output.

## Expected Behavior

After `make bazel_ci_test` completes, `bazel_collect` should be called to generate `bazel.xml` before the script checks for the file.

## References

- Jenkins job: https://prow.tidb.net/jenkins/job/pingcap/job/tidb/job/ghpr_unit_test/5764/
- Fix PR: #69476

Start by reading build/jenkins_unit_test.sh and build/jenkins_unit_test_ddlargsv1.sh, then run or inspect the ghpr_unit_test flow around make bazel_ci_test and the bazel.xml check. Done means bazel_collect runs after the test command and bazel.xml is available for junit artifact collection in both scripts.

Written by the indexing model from the issue text.