fix: Misspelled Variable Name (#1662)

### What problem does this PR solve?


### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

rag/app/qa.py

             if not has_bull:  # No question bullet
                 if not last_q:
                     if tbl_pn < line_pn or (tbl_pn == line_pn and tbl_top <= line_top):    # image passed
-                        tbls_index += 1
+                        tbl_index += 1
                     continue
                 else:
                     sum_tag = line_tag