gh-101117: Improve accuracy of sqlite3.Cursor.rowcount docs (#104287)

The SQLite C API sqlite3_changes() can only be relied upon when the
current active statement has been run to completion.

Author: erlend-aasland

Doc/library/sqlite3.rst

@@ -1694,7 +1694,10 @@ Cursor objects
       ``INSERT``, ``UPDATE``, ``DELETE``, and ``REPLACE`` statements;
       is ``-1`` for other statements,
       including :abbr:`CTE (Common Table Expression)` queries.
-      It is only updated by the :meth:`execute` and :meth:`executemany` methods.
+      It is only updated by the :meth:`execute` and :meth:`executemany` methods,
+      after the statement has run to completion.
+      This means that any resulting rows must be fetched in order for
+      :attr:`!rowcount` to be updated.
 
    .. attribute:: row_factory