fix: clean up .gitlab-ci.yml by removing unused variables and improving script organization

variables:

  DOCKER_DRIVER: overlay2

  DOCKER_TLS_CERTDIR: ""

  FORGE_REGISTRY: forge.etsi.org:5050

build_image:

  stage: build

    - docker push $IMAGE_NAME:$CI_COMMIT_SHA

    - docker push $IMAGE_NAME:cache

    - echo "IMAGE_TAG=$CI_COMMIT_SHA" > build.env

    - echo "IMAGE_NAME=$IMAGE_NAME" >> build.env

    - cat build.env

  artifacts:

    expire_in: 1 week

    reports:

      dotenv: build.env

  after_script:

    - export IMAGE_NAME="$CI_REGISTRY/$(echo $CI_PROJECT_PATH | tr '[:upper:]' '[:lower:]')"

    - echo "IMAGE_TAG=$CI_COMMIT_SHA" >> build.env

    - echo "IMAGE_NAME=$IMAGE_NAME" >> build.env

test_documentation:

  stage: test

  image: $IMAGE_NAME:$IMAGE_TAG

  needs: ["build_image"]

  image: docker:25.0.3

  services:

    - docker:25.0.3-dind

  needs: 

    - job: build_image

      artifacts: true

  rules:

    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'

    - if: '$CI_COMMIT_BRANCH == "develop"'

    - when: never

  variables:

    GIT_STRATEGY: clone

  before_script:

    - echo "IMAGE_NAME from artifact = $IMAGE_NAME"

    - echo "IMAGE_TAG from artifact = $IMAGE_TAG"

    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY

    - docker pull $IMAGE_NAME:$IMAGE_TAG

  script:

    - ls -la

    - python -m unittest discover -s ./doc/tests -t ./doc

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    - echo "Running tests in container..."

    - docker run --rm -v $CI_PROJECT_DIR:/workspace -w /workspace $IMAGE_NAME:$IMAGE_TAG python -m unittest discover -s ./doc/tests -t ./doc

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