update python to 3.9, fix gitlab-ci test step

.gitlab-ci.yml

@@ -16,7 +16,7 @@ install:
         expire_in: 1 week
 
 test:
-    image: python:3.7
+    image: python:3.9
     stage: test
     needs: []
     services:
@@ -28,14 +28,15 @@ test:
         DATABASE_URL: "postgresql://postgres:postgres@postgres:5432/$POSTGRES_DB"
         DB_HOST: postgres
     script:
-        - python -V
-        - pip install -r requirements.txt
+        - pip install poetry==1.1.4
+        - poetry config virtualenvs.create false
+        - poetry install --no-dev --no-interaction --no-ansi
         - python manage.py migrate --noinput
         - python manage.py createdefaultadmin
         - python manage.py test
 
 lint:py:
-    image: python:3.7
+    image: python:3.9
     stage: lint
     needs: []
     script: