Deprecate pytest yield fixtures.

https://docs.pytest.org/en/latest/yieldfixture.html

{{cookiecutter.app_name}}/tests/conftest.py

@@ -11,7 +11,7 @@ from {{cookiecutter.app_name}}.settings import TestConfig
 from .factories import UserFactory
 
 
-@pytest.yield_fixture(scope='function')
+@pytest.fixture
 def app():
     """An application for the tests."""
     _app = create_app(TestConfig)
@@ -23,13 +23,13 @@ def app():
     ctx.pop()
 
 
-@pytest.fixture(scope='function')
+@pytest.fixture
 def testapp(app):
     """A Webtest app."""
     return TestApp(app)
 
 
-@pytest.yield_fixture(scope='function')
+@pytest.fixture
 def db(app):
     """A database for the tests."""
     _db.app = app