Speed-up CI by merging static checks

For each job, the whole setup process has to be run. To reduce that impact, both static checks for code and migrations are run in one job

.gitlab-ci.yml

@@ -28,9 +28,6 @@ before_script:
 check:
   script:
     - ./Utils/check.sh --all
-
-check-migrations:
-  script:
     - source venv/bin/activate
     - ./manage.py makemigrations --dry-run --check