CI: use fsl-ci-rules infrastructure for testing

.gitlab-ci.yml

-include:
- - file: .gitlab-ci.yml
-   project: fsl/conda/fsl-ci-rules
-
-stages:
- - test
- - fsl-ci-pre
- - fsl-ci-build
- - fsl-ci-test
- - fsl-ci-deploy
-
-test:linux:
-  image: python:3.7
-  except:
-   - tags
-   - master@fsl/base
-  script:
-   - pip install pytest
-   - pytest -v tests
-  stage: test
-  tags:
-   - docker
-
-test:macos:
-  image: python:3.7
-  except:
-   - tags
-   - master@fsl/base
-  script:
-   - pip install pytest
-   - pytest -v tests
-  stage: test
-  tags:
-   - macOS
-   - shell
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