fix: use custom image having tox already installed

templates/lint/black.yml

 ---
 black:
   interruptible: true
-  before_script:
-    - pip install tox
+  image: registry.logilab.fr/logilab/infra/dockerfiles/debian-buster-slim-pg11
   stage: lint
   script: tox -e black

templates/lint/check-manifest.yml

 ---
 check-manifest:
   interruptible: true
-  before_script:
-    - pip install tox
+  image: registry.logilab.fr/logilab/infra/dockerfiles/debian-buster-slim-pg11
   stage: lint
   script: tox -e check-manifest

templates/lint/flake8.yml

 ---
 flake8:
   interruptible: true
-  before_script:
-    - pip install tox flake8-gl-codeclimate
+  image: registry.logilab.fr/logilab/infra/dockerfiles/debian-buster-slim-pg11
   stage: lint
   script:
     - tox -e flake8 -- --exit-zero --format gl-codeclimate --output-file gl-code-quality-report.json

templates/lint/mypy.yml

 ---
 mypy:
   interruptible: true
-  before_script:
-    - pip install tox
+  image: registry.logilab.fr/logilab/infra/dockerfiles/debian-buster-slim-pg11
   stage: lint
   allow_failure: true
   script: tox -e mypy

templates/lint/safety.yml

@@ -2,6 +2,5 @@
 safety:
   interruptible: true
   stage: lint
-  before_script:
-    - pip install tox
+  image: registry.logilab.fr/logilab/infra/dockerfiles/debian-buster-slim-pg11
   script: tox -e safety

templates/lint/yamllint.yml

 ---
 yamllint:
   interruptible: true
-  before_script:
-    - pip install tox
+  image: registry.logilab.fr/logilab/infra/dockerfiles/debian-buster-slim-pg11
   stage: lint
   rules:
     - changes:

templates/tests/py3.yml

 ---
 py3:
   interruptible: true
-  before_script:
-    - pip install tox
+  image: registry.logilab.fr/logilab/infra/dockerfiles/debian-buster-slim-pg11
   stage: tests
   script: tox -e py3 -- --junitxml=report.xml
   artifacts:

templates/upload-to-pypi.yml

 ---
 pypi-publish:
   stage: publish
+  image: registry.logilab.fr/logilab/infra/dockerfiles/debian-buster-slim-pg11
   rules:
     - if: '$CI_MERGE_REQUEST_ID'
       when: never
     - if: '$CI_COMMIT_TAG'
       when: on_success
   script:
@@ -4,8 +5,7 @@
   rules:
     - if: '$CI_MERGE_REQUEST_ID'
       when: never
     - if: '$CI_COMMIT_TAG'
       when: on_success
   script:
-    - pip install tox
     - tox -e pypi-publish