[ci] #118: Stop installing all dependencies into jobs for one dev dep:

- mypy, pylint, and sphinx are now directly installed in v3.8 container
- This in order to speed-up the jobs

.gitlab-ci.yml

@@ -57,7 +57,6 @@ type:
     - .changes
   stage: checks
   script:
-    - poetry install
     - make mypy
 
 lint:
@@ -65,7 +64,6 @@ lint:
     - .changes
   stage: checks
   script:
-    - poetry install
     - make pylint
 
 .tests:
@@ -124,7 +122,6 @@ pages:
     - tags
     - master
   script:
-    - poetry install
     - make docs
     - mv docs/_build/html public
     - ls public