Bug 1789684 - Fix decision.py reference to create.testing r=ahal

Decision was creating a shallow copy of create.testing at import time
Referencing the module variable fixes it

Differential Revision: https://phabricator.services.mozilla.com/D156714

taskcluster/gecko_taskgraph/decision.py

@@ -13,7 +13,8 @@ from collections import defaultdict
 
 import yaml
 from redo import retry
-from taskgraph.create import create_tasks, testing
+from taskgraph import create
+from taskgraph.create import create_tasks
 from taskgraph.decision import (
     # TODO: Let standalone taskgraph generate parameters instead
     # of calling internals
@@ -217,7 +218,7 @@ def taskgraph_decision(options, parameters=None):
         write_artifacts=True,
     )
 
-    if not testing:
+    if not create.testing:
         # set additional index paths for the decision task
         set_decision_indexes(decision_task_id, tgg.parameters, tgg.graph_config)