Workaround for pytest bug.

pytest 7.0.0 does not work with python 3.9. Exclude that specific combo.
From: pytest-dev/pytest#9608 (comment)

Author: DanLipsitt

tests/dev.requirements.txt

@@ -12,7 +12,9 @@ sqlalchemy_utils==0.36.8
 gino-starlette==0.1.1
 
 # Testing
-pytest
+openapi-spec-validator
+pytest; python_version != '3.9'
+pytest !=7.0.0; python_version == '3.9'
 pytest-virtualenv
 requests
 asynctest