state compiler: relax aggregate conditional check

Fixes #27961.

salt/state.py

@@ -652,7 +652,7 @@ class State(object):
         Execute the aggregation systems to runtime modify the low chunk
         '''
         agg_opt = self.functions['config.option']('state_aggregate')
-        if low.get('aggregate') is True:
+        if 'aggregate' in low:
             agg_opt = low['aggregate']
         if agg_opt is True:
             agg_opt = [low['state']]