[FIX] mail: _finalize_tracking was not properly flushed

Before this commit, no recompulation were performed at the end of the
tracking procedure.  This is because the main flush() occurred before
the tracking of values.  The absence of flushing is problematic in the
case where the tracking is used to create/update records.

closes odoo/odoo#44851

X-original-commit: c60da49a1d81fa73b60135185d5b706eec771475
Signed-off-by: Raphael Collet (rco) <rco@openerp.com>