use pytest-env for GH actions

.github/workflows/doctest-package.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install flake8 pytest
+        pip install flake8 pytest pytest-env
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
         pip install flybrains --no-deps
     - name: Install navis

pytest.ini

@@ -1,3 +1,5 @@
 [pytest]
 doctest_optionflags = IGNORE_EXCEPTION_DETAIL NUMBER NORMALIZE_WHITESPACE
 addopts = --doctest-modules
+env =
+    NAVIS_HEADLESS=TRUE