Do not aggregate TestReport when using matrix job

Ref: #296814 (closed)

What does this MR do and why?

This MR fixes a typebug where all parallel matrix jobs are aggregated in 1 job.

Why are we doing this?

When using parallel jobs we aggregate all specs using build#group_name when building our TestReport.

This makes sense for gitlab.com where all jobs running are parallelized to speed things up, as you can see on this page.

However the team decided to not aggregate multiple TestSuite results when users are using a matrix job so users can generate test reports correctly using matrix jobs.

Screenshots or screen recordings

Ressource	Before	After
Pipeline
Merge Request

Testing locally

1. Create a job using the gitlab-ci.yml provided below
2. Verify test report result is not being aggregated on http://localhost:3000/root/<PROJECT_ID>/-/pipelines/<PIPELINE_ID>/test_report
3. Verify test report result is not being aggregated on the MR widget

---

gitlab-ci.yml

matrix:
  parallel:
    matrix:
      - ID: ["1", "2"]
  script:
    - ls
  artifacts:
    when: always
    paths:
      - report-${ID}.xml
    reports:
      junit:
        - report-${ID}.xml

report-1.xml

<?xml version="1.0"?>
<testsuite errors="0" failures="1" tests="2" name="from cppunit">
  <testcase classname="EventConstsTest" name="TestRecFitQuality">
    <failure message="assertion failed" type="Assertion">assertion failed
      One type of problem
Line: test.cc:23</failure>
  </testcase>
  <testcase classname="EventConstsTest" name="TestRecTrackConst"/>
</testsuite>

MR acceptance checklist

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