[FIX] base: Allow users read_group with reified field inside the view

Until now using a groupby on a view containing a reified field added
with studio was not possible.

Because `read_group` uses these pseudofields as simple fields when they
are not actually columns in the table.

With `read`, `write`, `create` and `fields_get` it was already
supported.

This commit solves this problem by ignoring reified fields in an
override of `read_group`

opw-2793148

closes odoo/odoo#87120

X-original-commit: 48f869b6
Signed-off-by: Raphael Collet <rco@odoo.com>