gitlab: update centos-8-stream job

A couple of clean-ups here:

  - inherit from the custom runners job for artefacts
  - call check-avocado directly
  - add some comments to the top about setup

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230315174331.2959-6-alex.bennee@linaro.org>

.gitlab-ci.d/custom-runners/centos-stream-8-x86_64.yml

@@ -1,4 +1,9 @@
+# All centos-stream-8 jobs should run successfully in an environment
+# setup by the scripts/ci/setup/stream/8/build-environment.yml task
+# "Installation of extra packages to build QEMU"
+
 centos-stream-8-x86_64:
+ extends: .custom_runner_template
  allow_failure: true
  needs: []
  stage: build
@@ -8,15 +13,6 @@ centos-stream-8-x86_64:
  rules:
  - if: '$CI_PROJECT_NAMESPACE == "qemu-project" && $CI_COMMIT_BRANCH =~ /^staging/'
  - if: "$CENTOS_STREAM_8_x86_64_RUNNER_AVAILABLE"
- artifacts:
-   name: "$CI_JOB_NAME-$CI_COMMIT_REF_SLUG"
-   when: on_failure
-   expire_in: 7 days
-   paths:
-     - build/tests/results/latest/results.xml
-     - build/tests/results/latest/test-results
-   reports:
-     junit: build/tests/results/latest/results.xml
  before_script:
  - JOBS=$(expr $(nproc) + 1)
  script:
@@ -25,6 +21,4 @@ centos-stream-8-x86_64:
  - ../scripts/ci/org.centos/stream/8/x86_64/configure
    || { cat config.log meson-logs/meson-log.txt; exit 1; }
  - make -j"$JOBS"
- - make NINJA=":" check
-   || { cat meson-logs/testlog.txt; exit 1; } ;
- - ../scripts/ci/org.centos/stream/8/x86_64/test-avocado
+ - make NINJA=":" check check-avocado