Python: Apply suggestions from code review

Co-authored-by: yoff <lerchedahl@gmail.com>

python/ql/test/library-tests/frameworks/requests/taint_test.py

@@ -17,6 +17,7 @@ def test_taint(): # $ requestHandler
     requests.models.Response
 
     ensure_tainted(
+        url, # $ tainted
         # see https://docs.python-requests.org/en/latest/api/#requests.Response
         resp, # $ tainted
         resp.text, # $ tainted