[FIX] mail: fix get_sys_logs to have the same behaviour than previous version

After convertion python2 to python3, the arg0 was send as dict instead
of one string. We prefer to keep the same behaviour that previously.

addons/mail/models/update.py

@@ -13,8 +13,7 @@ from odoo import api, release, SUPERUSER_ID
 from odoo.exceptions import UserError
 from odoo.models import AbstractModel
 from odoo.tools.translate import _
-from odoo.tools import config
-from odoo.tools import misc
+from odoo.tools import config, misc, ustr
 
 _logger = logging.getLogger(__name__)
 
@@ -71,7 +70,7 @@ class PublisherWarrantyContract(AbstractModel):
         Utility method to send a publisher warranty get logs messages.
         """
         msg = self._get_message()
-        arguments = {'arg0': msg, "action": "update"}
+        arguments = {'arg0': ustr(msg), "action": "update"}
 
         url = config.get("publisher_warranty_url")