fix: correct test template to use args[1] for URL and keep_blank_values

Author: taimo3810

gapic/templates/tests/unit/gapic/%name_%version/%sub/test_macros.j2

@@ -1201,9 +1201,10 @@ def test_{{ method_name }}_rest_required_fields(request_type={{ method.input.ide
               {% endif %}
             ]
             # Verify query params are correctly included in the URL
-            actual_url = req.call_args.args[0]
+            # Session.request is called as request(method, url, ...), so url is args[1]
+            actual_url = req.call_args.args[1]
             parsed_url = urllib.parse.urlparse(actual_url)
-            actual_params = urllib.parse.parse_qsl(parsed_url.query)
+            actual_params = urllib.parse.parse_qsl(parsed_url.query, keep_blank_values=True)
             assert set(expected_params).issubset(set(actual_params))