send same sub_stmt to after_cursor_execute as before

send same sub_stmt to after_cursor_execute as before

Fixed issue in the :meth:`.ConnectionEvents.after_cursor_execute` method
where the SQL statement and parameter list for an "insertmanyvalues"
operation sent to the event would not be the actual SQL / parameters just
emitted on the cursor, instead being the non-batched form of the statement
that's used as a template to generate the batched statements.

Fixes: #13018
Change-Id: Ib5b6c576f2c7a9ed275de30290d619cc651b4816