Fix OpenAPI CI job using wrong DRF version

.gitlab-ci.yml

@@ -50,7 +50,7 @@ backend-openapi:
   before_script: []
   script:
     - mkdir -p output
-    - pip install -e .
+    - pip install --no-deps -e .
     - arkindex/manage.py generateschema > output/original.yml
     - openapi/patch.py openapi/patch.yml output/original.yml > output/schema.yml