fix(integrations/dramatiq): use set_transaction_name (#4175)

The Dramatiq integration is using a deprecated method to set the scope's
transaction name, use set_transaction_name instead.

"Assigning to scope.transaction directly is deprecated: use
scope.set_transaction_name() instead."

Author: timdrijvers

Diff for: sentry_sdk/integrations/dramatiq.py

@@ -95,7 +95,7 @@ def before_process_message(self, broker, message):
         message._scope_manager.__enter__()
 
         scope = sentry_sdk.get_current_scope()
-        scope.transaction = message.actor_name
+        scope.set_transaction_name(message.actor_name)
         scope.set_extra("dramatiq_message_id", message.message_id)
         scope.add_event_processor(_make_message_event_processor(message, integration))