Make Django test optional

conftest.py

@@ -147,6 +147,12 @@ def has_typing(environment):
     return bool(script.infer())
 
 
+@pytest.fixture(scope='session')
+def has_django(environment):
+    script = jedi.Script('import django', environment=environment)
+    return bool(script.infer())
+
+
 @pytest.fixture(scope='session')
 def jedi_path():
     return os.path.dirname(__file__)