Skip trigger using contextual key

Relying on the user is not flexible enough.

issue8993
review260841002

trytond/ir/trigger.py

@@ -147,7 +147,7 @@ class Trigger(DeactivableMixin, ModelSQL, ModelView):
         assert mode in ['create', 'write', 'delete', 'time'], \
             'Invalid trigger mode'
 
-        if Transaction().user == 0 and not Transaction().context.get('user'):
+        if Transaction().context.get('_no_trigger'):
             return []
 
         key = (model_name, mode)

trytond/modules/__init__.py

@@ -352,7 +352,8 @@ def load_modules(
         global res
         transaction = Transaction()
 
-        with transaction.connection.cursor() as cursor:
+        with transaction.set_context(_no_trigger=True), \
+                transaction.connection.cursor() as cursor:
             # Migration from 3.6: remove double module
             old_table = 'ir_module_module'
             new_table = 'ir_module'