[FIX] core: missing escaping in sql constraint name_manual_field

Oversight in revision
8c38baee85

In SQL,
The underscore character ( _ ) represents a single character
to match a pattern from a word or string.

Meaning
`name LIKE 'x_%'`
allows names starting by `x`, and not names starting by `x_` as expected.

Add the escape in the constraint to enforce starting by `x_`
and not just `x`

closes odoo/odoo#127883

odoo/addons/base/models/ir_model.py

@@ -610,7 +610,7 @@ class IrModelFields(models.Model):
         ('size_gt_zero', 'CHECK (size>=0)', 'Size of the field cannot be negative.'),
         (
             "name_manual_field",
-            "CHECK (state != 'manual' OR name LIKE 'x_%')",
+            "CHECK (state != 'manual' OR name LIKE 'x\\_%')",
             "Custom fields must have a name that starts with 'x_'!"
         ),
     ]

odoo/addons/base/tests/test_ir_actions.py

@@ -380,13 +380,13 @@ class TestCustomFields(common.TransactionCase):
     def test_create_custom(self):
         """ custom field names must be start with 'x_' """
         with self.assertRaises(IntegrityError), mute_logger('odoo.sql_db'):
-            self.create_field('foo')
+            self.create_field('xyz')
 
     def test_rename_custom(self):
         """ custom field names must be start with 'x_' """
-        field = self.create_field('x_foo')
+        field = self.create_field('x_xyz')
         with self.assertRaises(IntegrityError), mute_logger('odoo.sql_db'):
-            field.name = 'foo'
+            field.name = 'xyz'
 
     def test_create_valid(self):
         """ field names must be valid pg identifiers """