[FIX] base: in res.config.settings, field.related is a string

It used to be a tuple.
Cf: 1abe965b59

opw-2681777

closes odoo/odoo#81312

X-original-commit: aa74f51db7bf5a8ad1f4e309b6352df3c31037ec
Signed-off-by: Raphael Collet <rco@odoo.com>

odoo/addons/base/models/res_config.py

@@ -776,7 +776,7 @@ class ResConfigSettings(models.TransientModel, ResConfigModuleInstallationMixin)
                 continue
             # we write on a related field like
             # qr_code = fields.Boolean(related='company_id.qr_code', readonly=False)
-            fname0 = field.related[0]
+            fname0, *fnames = field.related.split(".")
             if fname0 not in values:
                 continue
 
@@ -784,7 +784,7 @@ class ResConfigSettings(models.TransientModel, ResConfigModuleInstallationMixin)
             field0 = self._fields[fname0]
             old_value = field0.convert_to_record(
                 field0.convert_to_cache(values[fname0], self), self)
-            for fname in field.related[1:]:
+            for fname in fnames:
                 old_value = next(iter(old_value), old_value)[fname]
 
             # determine the new value