Don't run tests in parallel

Author: stevebux

Makefile

@@ -134,7 +134,6 @@ TEST_CMD := APIGEE_ACCESS_TOKEN="$(APIGEE_ACCESS_TOKEN)" \
 	STATUS_ENDPOINT_API_KEY="$(STATUS_ENDPOINT_API_KEY)" \
 	PYTHONPATH=. poetry run pytest --disable-warnings -vv \
 	--color=yes \
-	-n 4 \
 	--api-name=nhs-notify-supplier \
 	--proxy-name="$(PROXY_NAME)" \
 	-s \