make sure tox passes the PYTEST_ADDOPTS env

Author: selmanozleyen

tox.ini

@@ -80,7 +80,7 @@ extras =
     interactive
     test
 setenv = linux: PYTEST_FLAGS=--test-napari
-passenv = TOXENV,CI,CODECOV_*,GITHUB_ACTIONS,PYTEST_FLAGS,DISPLAY,XAUTHORITY,MPLBACKEND
+passenv = TOXENV,CI,CODECOV_*,GITHUB_ACTIONS,PYTEST_FLAGS,DISPLAY,XAUTHORITY,MPLBACKEND,PYTEST_ADDOPTS
 usedevelop = true
 commands =
     python -m pytest --color=yes --cov --cov-append --cov-report=xml --cov-config={toxinidir}/tox.ini --ignore docs/ {posargs:-vv} {env:PYTEST_FLAGS:}