[ci] #162: Add isort job

isort is installed on 3.8 image

.gitlab-ci.yml

@@ -41,6 +41,13 @@ build:
   script:
     - poetry build
 
+isort:
+  extends:
+    - .code_changes
+  stage: checks
+  script:
+    - isort --check duniterpy tests examples
+
 type:
   extends:
     - .code_changes