Avoid selenium deprecation warning when testing

Switch from setting the options.headless attribute to calling
options.add_argument("-headless").  See [1] for more info.

[1] https://www.selenium.dev/blog/2023/headless-is-going-away/

Author: living180

tests/test_integration.py

@@ -533,7 +533,8 @@ class DebugToolbarLiveTestCase(StaticLiveServerTestCase):
     def setUpClass(cls):
         super().setUpClass()
         options = Options()
-        options.headless = bool(os.environ.get("CI"))
+        if os.environ.get("CI"):
+            options.add_argument("-headless")
         cls.selenium = webdriver.Firefox(options=options)
 
     @classmethod

tox.ini

@@ -23,7 +23,7 @@ deps =
     Jinja2
     html5lib
     pygments
-    selenium
+    selenium>=4.8.0
     sqlparse
 passenv=
     CI