added headless option to .test_sharing for woodpecker FT run

src/functional_tests/test_sharing.py

@@ -1,3 +1,5 @@
+import os
+
 from selenium import webdriver
 from selenium.webdriver.common.by import By
 
@@ -21,7 +23,10 @@ class SharingTest(FunctionalTest):
         disco_browser = self.browser
         self.addCleanup(lambda: quit_if_possible(disco_browser))
 
-        ali_browser = webdriver.Firefox()
+        options = webdriver.FirefoxOptions()
+        if os.environ.get("HEADLESS"):
+            options.add_argument("--headless")
+        ali_browser = webdriver.Firefox(options=options)
         self.addCleanup(lambda: quit_if_possible(ali_browser))
         self.browser = ali_browser
         self.create_pre_authenticated_session("alice@example.com")