[FIX] base: flatten if ir.model.field.selection selection ids

The `get_technical_translations()` method was returning wrong list of list
for field selection values; instead we flatten the results to get a correct
domain.

closes odoo/odoo#37101

Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>

odoo/addons/base/models/ir_translation.py

@@ -832,7 +832,7 @@ class IrTranslation(models.Model):
         :return: action definition to open the list of available translations
         """
         fields = self.env['ir.model.fields'].search([('model', '=', model_name)])
-        selection_ids = [field.selection_ids.ids for field in fields if field.ttype == 'selection']
+        selection_ids = tools.flatten([field.selection_ids.ids for field in fields if field.ttype == 'selection'])
         view = self.env.ref("base.view_translation_tree", False) or self.env['ir.ui.view']
         return {
             'name': _("Technical Translations"),