downgrade pytest to 5.3.5 to fix issue with pytest_sugar

see: Teemu/pytest-sugar#187

requirements_test.in

@@ -7,7 +7,7 @@ allure-pytest
 pillow
 selenium
 locustio
-pytest
+pytest==5.3.5
 pytest-cov
 pytest-django
 pytest-sugar

requirements_test.txt

@@ -110,7 +110,7 @@ pyrsistent==0.15.7        # via jsonschema
 pytest-cov==2.8.1         # via -r requirements_test.in
 pytest-django==3.8.0      # via -r requirements_test.in
 pytest-sugar==0.9.2       # via -r requirements_test.in
-pytest==5.4.1             # via -r requirements_test.in, allure-pytest, pytest-cov, pytest-django, pytest-sugar
+pytest==5.3.5             # via -r requirements_test.in, allure-pytest, pytest-cov, pytest-django, pytest-sugar
 python-dateutil==2.8.1    # via botocore, faker, freezegun
 pytz==2019.3              # via django, django-modelcluster, wagtail
 pyzmq==19.0.0             # via locustio