Invoke sugar also on CI, but not enable it by default

This way it's possible to disable it with using

    pytest -p no:sugar

and this can be useful since, for example, hypothesis statistics are not
showed: https://github.com/Teemu/pytest-sugar/issues/221

.drone.yml

@@ -11,4 +11,4 @@ steps:
       - curl -sSL https://raw.githubusercontent.com/python-poetry/poetry/master/get-poetry.py | python -
       - export PATH=$PATH:$HOME/.poetry/bin
       - poetry install
-      - poetry run pytest
+      - poetry run pytest --force-sugar

pyproject.toml

@@ -17,7 +17,7 @@ pytest-xdist = "^2.2.1"
 
 [tool.pytest.ini_options]
 minversion = "6.0"
-addopts = "--verbose --force-sugar"
+addopts = "--verbose"
 
 [build-system]
 requires = ["poetry-core>=1.0.0"]