[FIX] fields: convert selection value to int

When a string value is assigned to a selection field expecting integers, the
value simply rejected.  In such a case, convert the value to an integer before
validating it.

odoo/fields.py

@@ -1798,6 +1798,8 @@ class Selection(Field):
     def convert_to_cache(self, value, record, validate=True):
         if not validate:
             return value or False
+        if value and self.column_type[0] == 'int4':
+            value = int(value)
         if value in self.get_values(record.env):
             return value
         elif not value: