Tweak row num due to walrus

Author: hjwp

chapter_16_advanced_forms.asciidoc

@@ -1011,7 +1011,7 @@ Traceback (most recent call last):
   File "...goat-book/src/functional_tests/test_list_item_validation.py", line
 47, in test_cannot_add_empty_list_items
     self.wait_for_row_in_list_table("2: Make tea")
-  File "...goat-book/src/functional_tests/base.py", line 38, in
+  File "...goat-book/src/functional_tests/base.py", line 37, in
 wait_for_row_in_list_table
     self.assertIn(row_text, [row.text for row in rows])
 AssertionError: '2: Make tea' not found in ['1: Make tea', '2: Purchase milk']